Article 250

Grounding and Bonding

Part I. General

Scope. This article covers general requirements for grounding and bonding of electrical installations, and the specific requirements in (1) through (6).
1. Systems, circuits, and equipment required, permitted, or not permitted to be grounded
2. Circuit conductor to be grounded on grounded systems
3. Location of grounding connections
4. Types and sizes of grounding and bonding conductors and electrodes
5. Methods of grounding and bonding
6. Conditions under which guards, isolation, or insulation may be substituted for grounding
Informational Note: See Figure 250.1 for information on the organization of Article 250 covering grounding and bonding requirements.
Definition.Bonding Jumper, Supply-Side. A conductor installed on the supply side of a service or within a service equipment enclo‐ sure(s), or for a separately derived system, that ensures the required electrical conductivity between metal parts required to be electrically connected.
Application of Other Articles. For other articles apply‐ ing to particular cases of installation of conductors and equip‐ ment, grounding and bonding requirements are identified in Table 250.3 that are in addition to, or modifications of, those of this article.
General Requirements for Grounding and Bonding. The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

Grounded Systems.
1. Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or uninten‐ tional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.Informational Note No. 1: An important consideration for limit‐ ing the imposed voltage is the routing of bonding and ground‐ ing electrode conductors so that they are not any longer than necessary to complete the connection without disturbing the permanent parts of the installation and so that unnecessary bends and loops are avoided.Informational Note No. 2: See NFPA 780-2014, Standard for the Installation of Lightning Protection Systems, for information on
  
  installation of grounding and bonding for lightning protectionsystems.
2. Grounding of Electrical Equipment. Normally non– current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.
3. Bonding of Electrical Equipment. Normally non–current- carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
4. Bonding of Electrically Conductive Materials and Other Equipment. Normally non–current-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.
5. Effective Ground-Fault Current Path. Electrical equip‐ ment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur
  
  Part I General
  
  Part II System grounding
  Part VIII Direct-current systemsPart X Grounding of systems and circuits of over 1000 voltsto the electrical supply source. The earth shall not be consid‐ ered as an effective ground-fault current path.
Ungrounded Systems.
1. Grounding Electrical Equipment. Non–current-carrying conductive materials enclosing electrical conductors or equip‐ ment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.
  Informational Note: See NFPA 780-2014, Standard for the Installa‐tion of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.
2. Bonding of Electrical Equipment. Non–current-carrying conductive materials enclosing electrical conductors or equip‐ ment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.
3. Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.Part III Grounding electrodesystem and grounding electrode conductorPart VII Methods of equipment groundingPart VI Equipment grounding and equipment grounding conductors
  Part V BondingPart IV Enclosure, raceway, and service cable grounding
4. Path for Fault Current. Electrical equipment, wiring, and other electrically conductive material likely to become ener‐ gized shall be installed in a manner that creates a low- impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcur‐ rent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path.

250.6 Objectionable Current.

Arrangement to Prevent Objectionable Current. The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non–current-carrying metal parts of equipment shall be instal‐ led and arranged in a manner that will prevent objectionable current.
Alterations to Stop Objectionable Current. If the use of multiple grounding connections results in objectionable current and the requirements of 250.4(A)(5) or (B)(4) are met, one or more of the following alterations shall be permit‐ ted:
1. Discontinue one or more but not all of such grounding connections.
2. Change the locations of the grounding connections.
3. Interrupt the continuity of the conductor or conductive path causing the objectionable current.
4. Take other suitable remedial and approved action.
Temporary Currents Not Classified as Objectionable Currents. Temporary currents resulting from abnormal condi‐ tions, such as ground faults, shall not be classified as objection‐ able current for the purposes specified in 250.6(A) and (B).

Part IX Instruments, meters, and relays

FIGURE 250.1 Grounding and Bonding.

Table 250.3 Additional Grounding and Bonding Requirements

Conductor/Equipment Article Section

Agricultural buildings 547.9 and 547.10

reproduction equipment
Branch circuits		210.5, 210.6, 406.3
Cablebus		370.9
Cable trays	392	392.60
Capacitors		460.10, 460.27
Circuits and equipment operating at less than 50 volts	720
Communications circuits	800
Community antenna television and radio distribution		820.93, 820.100, 820.103, 820.106
systems
Conductors for general wiring	310
Cranes and hoists	610
Electrically driven or controlled irrigation machines		675.11(C), 675.12, 675.13, 675.14, 675.15
Electric signs and outline lighting	600
Electrolytic cells	668
Elevators, dumbwaiters, escalators, moving walks,	620

Audio signal processing, amplification, and 640.7

wheelchair lifts, and stairway chairlifts

Fixed electric heating equipment for pipelines and vessels

Fixed outdoor electric deicing and snow-melting equipment

427.29, 427.48

426.27

Flexible cords and cables	400.22, 400.23
Floating buildings	553.8, 553.10, 553.11
Grounding-type receptacles, adapters, cord	406.9
connectors, and attachment plugs
Hazardous (classified) locations	500–517
Health care facilities	517
Induction and dielectric heating equipment	665
Industrial machinery	670
Information technology equipment		645.15
Intrinsically safe systems		504.50
Luminaires and lighting equipment		410.40, 410.42, 410.46, 410.155(B)
Luminaires, lampholders, and lamps	410
Marinas and boatyards		555.15
Mobile homes and mobile home park	550
Motion picture and television studios and similar		530.20, 530.64(B)
locations
Motors, motor circuits, and controllers	430
Natural and artificially made bodies of water	682	682.30, 682.31, 682.32, 682.33
Network powered broadband communications circuits		830.93, 830.100, 830.106
Optical fiber cables		770.100
Outlet, device, pull, and junction boxes; conduit		314.4, 314.25
bodies; and fittings
Over 600 volts, nominal, underground wiring methods		300.50(C)
Panelboards		408.40
Pipe organs	650
Radio and television equipment	810
Receptacles and cord connectors		406.3
Recreational vehicles and recreational vehicle parks	551
Services	230
Solar photovoltaic systems		690.41, 690.42, 690.43, 690.45, 690.47
Swimming pools, fountains, and similar installations	680
Switchboards and panelboards		408.3(D)
Switches		404.12
Theaters, audience areas of motion picture and		520.81
television studios, and similar locations
Transformers and transformer vaults		450.10
Use and identification of grounded conductors	200
X-ray equipment	660	517.78

Limitations to Permissible Alterations. The provisions of this section shall not be considered as permitting electronic equipment from being operated on ac systems or branch circuits that are not connected to an equipment grounding conductor as required by this article. Currents that introduce noise or data errors in electronic equipment shall not be considered the objectionable currents addressed in this section.
Isolation of Objectionable Direct-Current Ground Currents. Where isolation of objectionable dc ground currents from cathodic protection systems is required, a listed ac coupling/dc isolating device shall be permitted in the equip‐ ment grounding conductor path to provide an effective return path for ac ground-fault current while blocking dc current.

250.8 Connection of Grounding and Bonding Equipment.

Permitted Methods. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more of the following means:
1. Listed pressure connectors
2. Terminal bars
3. Pressure connectors listed as grounding and bonding equipment
4. Exothermic welding process
5. Machine screw-type fasteners that engage not less than two threads or are secured with a nut
6. Thread-forming machine screws that engage not less than two threads in the enclosure
7. Connections that are part of a listed assembly
8. Other listed means
Methods Not Permitted. Connection devices or fittings that depend solely on solder shall not be used.

250.10 Protection of Ground Clamps and Fittings. Ground clamps or other fittings exposed to physical damage shall be enclosed in metal, wood, or equivalent protective covering.

250.12 Clean Surfaces. Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded shall be removed from threads and other contact surfaces to ensure good electrical continuity or be connected by means of fittings designed so as to make such removal unnecessary.

Part II. System Grounding

Alternating-Current Systems to Be Grounded. Alternating-current systems shall be grounded as provided for in 250.20(A), (B), (C), or (D). Other systems shall be permit‐ ted to be grounded. If such systems are grounded, they shall comply with the applicable provisions of this article.Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. See 250.26(4) for conductor to be grounded.
1. Alternating-Current Systems of Less Than 50 Volts. Alternating-current systems of less than 50 volts shall be groun‐ ded under any of the following conditions:
  1. Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground
  2. Where supplied by transformers, if the transformer supply system is ungrounded
  3. Where installed outside as overhead conductors
2. Alternating-Current Systems of 50 Volts to 1000 Volts. Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions:
  1. Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts
  2. Where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conduc‐ tor
  3. Where the system is 3-phase, 4-wire, delta connected in which the midpoint of one phase winding is used as a circuit conductor
3. Alternating-Current Systems of over 1000 Volts. Alternating-current systems supplying mobile or portable equipment shall be grounded as specified in 250.188. Where supplying other than mobile or portable equipment, such systems shall be permitted to be grounded.
4. Impedance Grounded Neutral Systems. Impedance grounded neutral systems shall be grounded in accordance with 250.36 or 250.187.
Alternating-Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded.
1. General. The following ac systems of 50 volts to 1000 volts shall be permitted to be grounded but shall not be required to be grounded:
  1. Electrical systems used exclusively to supply industrial electric furnaces for melting, refining, tempering, and the like
  2. Separately derived systems used exclusively for rectifiers that supply only adjustable-speed industrial drives
  3. Separately derived systems supplied by transformers that have a primary voltage rating of 1000 volts or less if all the following conditions are met:
    1. The system is used exclusively for control circuits.
    2. The conditions of maintenance and supervision ensure that only qualified persons service the installa‐ tion.
    3. Continuity of control power is required.
  4. Other systems that are not required to be grounded in accordance with the requirements of 250.20(B)
2. Ground Detectors. Ground detectors shall be installed in accordance with 250.21(B)(1) and (B)(2).
  1. Ungrounded ac systems as permitted in 250.21(A)(1) through (A)(4) operating at not less than 120 volts and at 1000 volts or less shall have ground detectors installed on the system.
  2. The ground detection sensing equipment shall be connected as close as practicable to where the system receives its supply.
3. Marking. Ungrounded systems shall be legibly marked “Caution: Ungrounded System Operating — Volts Between Conductors” at the source or first disconnecting means of the system. The marking shall be of sufficient durabil‐ ity to withstand the environment involved.
Circuits Not to Be Grounded. The following circuits shall not be grounded:
1. Circuits for electric cranes operating over combustible fibers in Class III locations, as provided in 503.155
2. Circuits in health care facilities as provided in 517.61 and 517.160
3. Circuits for equipment within electrolytic cell line work‐ ing zones as provided in Article 668
4. Secondary circuits of lighting systems as provided in 411.6(A)
5. Secondary circuits of lighting systems as provided in 680.23(A)(2)

(6) Class 2 load side circuits for suspended ceiling low-voltage

power grid distribution systems as provided in 393.60(B)

250.24 Grounding Service-Supplied Alternating-Current Systems.

System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding elec‐ trode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5).
1. General. The grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, service drop, underground serv‐ ice conductors, or service lateral to, including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.Informational Note: See definitions of Service Conductors, Over‐ head; Service Conductors, Underground; Service Drop; and Service Lateral in Article 100.
2. Outdoor Transformer. Where the transformer supplying the service is located outside the building, at least one addi‐ tional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the trans‐ former or elsewhere outside the building.Exception: The additional grounding electrode conductor connection shall not be made on high-impedance grounded neutral systems. The system shall meet the requirements of 250.36.
3. Dual-Fed Services. For services that are dual fed (double ended) in a common enclosure or grouped together in sepa‐ rate enclosures and employing a secondary tie, a single ground‐ ing electrode conductor connection to the tie point of the grounded conductor(s) from each power source shall be permitted.
4. Main Bonding Jumper as Wire or Busbar. Where the main bonding jumper specified in 250.28 is a wire or busbar and is installed from the grounded conductor terminal bar or bus to the equipment grounding terminal bar or bus in the service equipment, the grounding electrode conductor shall be permitted to be connected to the equipment grounding termi‐ nal, bar, or bus to which the main bonding jumper is connec‐ ted.
5. Load-Side Grounding Connections. A grounded conduc‐ tor shall not be connected to normally non–current-carrying metal parts of equipment, to equipment grounding conduc‐ tor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article.Informational Note: See 250.30 for separately derived systems,250.32 for connections at separate buildings or structures, and250.142 for use of the grounded circuit conductor for ground‐ ing equipment.
Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28.Exception No. 1: Where more than one service disconnecting means is located in an assembly listed for use as service equipment, an unspliced main bonding jumper shall bond the grounded conductor(s) to the assembly enclosure.Exception No. 2: Impedance grounded neutral systems shall be permit‐ ted to be connected as provided in 250.36 and 250.187.
Grounded Conductor Brought to Service Equipment. Where an ac system operating at 1000 volts or less is grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each serv‐ ice disconnecting means enclosure. The grounded conduc‐ tor(s) shall be installed in accordance with 250.24(C)(1) through 250.24(C)(4).Exception: Where two or more service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to connect the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.
1. Sizing for a Single Raceway or Cable. The grounded conductor shall not be smaller than specified in Table 250.102(C)(1).
2. Parallel Conductors in Two or More Raceways or Cables. If the ungrounded service-entrance conductors are installed in parallel in two or more raceways or cables, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway or cable shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway or cable, as indicated in 250.24(C)(1), but not smaller than 1/0 AWG.Informational Note: See 310.10(H) for grounded conductors connected in parallel.
3. Delta-Connected Service. The grounded conductor of a 3- phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.
4. High Impedance. The grounded conductor on a high- impedance grounded neutral system shall be grounded in accordance with 250.36.
Grounding Electrode Conductor. A grounding electrode conductor shall be used to connect the equipment grounding conductors, the service-equipment enclosures, and, where the system is grounded, the grounded service conductor to the grounding electrode(s) required by Part III of this article. This conductor shall be sized in accordance with 250.66.High-impedance grounded neutral system connections shall be made as covered in 250.36.
Ungrounded System Grounding Connections. A premises wiring system that is supplied by an ac service that is ungroun‐ ded shall have, at each service, a grounding electrode conduc‐ tor connected to the grounding electrode(s) required by Part III of this article. The grounding electrode conductor shall be connected to a metal enclosure of the service conductors at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to the service disconnecting means.

250.26 Conductor to Be Grounded — Alternating-Current Systems. For ac premises wiring systems, the conductor to be grounded shall be as specified in the following:

Single-phase, 2-wire — one conductor
Single-phase, 3-wire — the neutral conductor
Multiphase systems having one wire common to all phases
- the neutral conductor
Multiphase systems where one phase is grounded — one phase conductor
Multiphase systems in which one phase is used as in (2)
- the neutral conductor

250.28 Main Bonding Jumper and System Bonding Jumper. For a grounded system, main bonding jumpers and system bonding jumpers shall be installed as follows:

Material. Main bonding jumpers and system bonding jumpers shall be of copper or other corrosion-resistant mate‐ rial. A main bonding jumper and a system bonding jumper shall be a wire, bus, screw, or similar suitable conductor.
Construction. Where a main bonding jumper or a system bonding jumper is a screw only, the screw shall be identified with a green finish that shall be visible with the screw installed.
Attachment. Main bonding jumpers and system bonding jumpers shall be connected in the manner specified by the applicable provisions of 250.8.
Size. Main bonding jumpers and system bonding jumpers shall be sized in accordance with 250.28(D)(1) through (D)(3).
1. General. Main bonding jumpers and system bonding jumpers shall not be smaller than specified in Table 250.102(C)(1).
2. Main Bonding Jumper for Service with More Than One Enclosure. Where a service consists of more than a single enclosure as permitted in 230.71(A), the main bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded service conduc‐ tor serving that enclosure.
3. Separately Derived System with More Than One Enclosure. Where a separately derived system supplies more than a single enclosure, the system bonding jumper for each enclosure shall be sized in accordance with 250.28(D)(1) based on the largest ungrounded feeder conductor serving that enclosure, or a single system bonding jumper shall be installed at the source and sized in accordance with 250.28(D)(1) based on the equiv‐ alent size of the largest supply conductor determined by the largest sum of the areas of the corresponding conductors of each set.

250.30 Grounding Separately Derived Alternating-Current Systems. In addition to complying with 250.30(A) for groun‐ ded systems, or as provided in 250.30(B) for ungrounded

systems, separately derived systems shall comply with 250.20, 250.21, 250.22, or 250.26, as applicable. Multiple separately derived systems that are connected in parallel shall be installed in accordance with 250.30.

Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service- supplied system grounded conductor. An example of such a situation is where alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served.

Informational Note No. 2: See 445.13 for the minimum size of conductors that carry fault current.

Grounded Systems. A separately derived ac system that is grounded shall comply with 250.30(A)(1) through (A)(8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non–current- carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper.Informational Note: See 250.32 for connections at separate buildings or structures and 250.142 for use of the grounded circuit conductor for grounding equipment.Exception: Impedance grounded neutral system grounding connections shall be made as specified in 250.36 or 250.187, as applicable.
1. System Bonding Jumper. An unspliced system bonding jumper shall comply with 250.28(A) through (D). This connec‐ tion shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices, in accordance with 250.30(A)(1)(a) or (b). The system bonding jumper shall remain within the enclo‐ sure where it originates. If the source is located outside the building or structure supplied, a system bonding jumper shall be installed at the grounding electrode connection in compli‐ ance with 250.30(C).Exception No. 1: For systems installed in accordance with 450.6, a single system bonding jumper connection to the tie point of the groun‐ ded circuit conductors from each power source shall be permitted.Exception No. 2: If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for the grounded conductor. If a grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a parallel path.Exception No. 3: The size of the system bonding jumper for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived ungrounded conductors and shall not be smaller than 14 AWG copper or 12 AWG aluminum.
  1. Installed at the Source. The system bonding jumper shall connect the grounded conductor to the supply-side bond‐ ing jumper and the normally non–current-carrying metal enclosure.
  2. Installed at the First Disconnecting Means. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper, the disconnecting means enclo‐ sure, and the equipment grounding conductor(s).
2. Supply-Side Bonding Jumper. If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means. A supply-side bonding jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permit‐ ted to be of nonflexible metal raceway type or of the wire or bus type as follows:
  1. A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors.
  2. A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bond‐ ing jumper of the wire type as determined in 250.102(C).Exception: A supply-side bonding jumper shall not be required between enclosures for installations made in compliance with 250.30(A)(1), Exception No. 2.
3. Grounded Conductor. If a grounded conductor is instal‐ led and the system bonding jumper connection is not located at the source, 250.30(A)(3)(a) through (A)(3)(d) shall apply.
  1. Sizing for a Single Raceway. The grounded conductor shall not be smaller than specified in Table 250.102(C)(1).
  2. Parallel Conductors in Two or More Raceways. If the ungrounded conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel derived ungrounded conductors in the raceway as indicated in 250.30(A)(3)(a), but not smaller than 1/0 AWG.Informational Note: See 310.10(H) for grounded conductors connected in parallel.
  3. Delta-Connected System. The grounded conductor of a 3-phase, 3-wire delta system shall have an ampacity not less than that of the ungrounded conductors.
  4. Impedance Grounded System. The grounded conductor of an impedance grounded neutral system shall be installed in accordance with 250.36 or 250.187, as applicable.
4. Grounding Electrode. The building or structure ground‐ ing electrode system shall be used as the grounding electrode for the separately derived system. If located outdoors, the grounding electrode shall be in accordance with 250.30(C) .•Exception: If a separately derived system originates in equipment thatis listed and identified as suitable for use as service equipment, the grounding electrode used for the service or feeder equipment shall be permitted to be used as the grounding electrode for the separately derived system.Informational Note No. 1: See 250.104(D) for bonding require‐ ments for interior metal water piping in the area served by sepa‐ rately derived systems.Informational Note No. 2: See 250.50 and 250.58 for require‐ ments for bonding all electrodes together if located at the same building or structure.
5. Grounding Electrode Conductor, Single Separately Derived System. A grounding electrode conductor for a single sepa‐rately derived system shall be sized in accordance with 250.66 for the derived ungrounded conductors. It shall be used to connect the grounded conductor of the derived system to the grounding electrode in accordance with 250.30(A)(4) , or as permitted in 250.68(C)(1) and (2). This connection shall be made at the same point on the separately derived system where the system bonding jumper is connected.Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor to the equipment grounding terminal, bar, or bus if the equipment grounding terminal, bar, or bus is of suffi‐ cient size for the separately derived system.Exception No. 2: If the source of a separately derived system is located within equipment listed and identified as suitable for use as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the ground‐ ing electrode conductor for the separately derived system, if the ground‐ ing electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the sepa‐ rately derived system, the grounding electrode connection for the sepa‐ rately derived system shall be permitted to be made to the bus.Exception No. 3: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Excep‐ tion No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134.
6. Grounding Electrode Conductor, Multiple Separately Derived Systems. A common grounding electrode conductor for multiple separately derived systems shall be permitted. If installed, the common grounding electrode conductor shall be used to connect the grounded conductor of the separately derived systems to the grounding electrode as specified in 250.30(A)(4). A grounding electrode conductor tap shall then be installed from each separately derived system to the common grounding electrode conductor. Each tap conductor shall connect the grounded conductor of the separately derived system to the common grounding electrode conductor. This connection shall be made at the same point on the sepa‐ rately derived system where the system bonding jumper is connected.Exception No. 1: If the system bonding jumper specified in 250.30(A)(1) is a wire or busbar, it shall be permitted to connect the grounding electrode conductor tap to the equipment grounding termi‐ nal, bar, or bus, provided the equipment grounding terminal, bar, or bus is of sufficient size for the separately derived system.Exception No. 2: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit and is derived from a transformer rated not more than 1000 volt-amperes, provided the system grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with 250.30(A)(1), Exception No. 3, and the transformer frame or enclosure is grounded by one of the means specified in 250.134.
  1. Common Grounding Electrode Conductor. The common grounding electrode conductor shall be permitted to be one of the following:
    1. A conductor of the wire type not smaller than 3/0 AWG copper or 250 kcmil aluminum
    2. A metal water pipe that complies with 250.68(C)(1)
    3. The metal structural frame of the building or structure that complies with 250.68(C)(2) or is connected to the grounding electrode system by a conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum
  2. Tap Conductor Size. Each tap conductor shall be sized in accordance with 250.66 based on the derived ungrounded conductors of the separately derived system it serves.Exception: If the source of a separately derived system is located within equipment listed and identified as suitable for use as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, if the grounding electrode conductor is of sufficient size for the separately derived system. If the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus.
  3. Connections. All tap connections to the common grounding electrode conductor shall be made at an accessible location by one of the following methods:
1. A connector listed as grounding and bonding equipment.
2. Listed connections to aluminum or copper busbars not smaller than 6 mm thick × 50 mm wide (1∕4 in. thick × 2 in. wide) and of sufficient length to accommodate the number of terminations necessary for the installation. If aluminum busbars are used, the installation shall also comply with 250.64(A).
3. The exothermic welding process.
Tap conductors shall be connected to the common ground‐ ing electrode conductor in such a manner that the common grounding electrode conductor remains without a splice or joint.
1. Installation. The installation of all grounding electrode conductors shall comply with 250.64(A), (B), (C), and (E).
2. Bonding. Structural steel and metal piping shall be connected to the grounded conductor of a separately derived system in accordance with 250.104(D).
Ungrounded Systems. The equipment of an ungrounded separately derived system shall be grounded and bonded as specified in 250.30(B)(1) through (B)(3).
1. Grounding Electrode Conductor. A grounding electrode conductor, sized in accordance with 250.66 for the largest derived ungrounded conductor(s) or set of derived ungroun‐ ded conductors, shall be used to connect the metal enclosures of the derived system to the grounding electrode as specified in 250.30(A)(5) or (6), as applicable. This connection shall be made at any point on the separately derived system from the source to the first system disconnecting means. If the source is located outside the building or structure supplied, a grounding electrode connection shall be made in compliance with 250.30(C).
2. Grounding Electrode. Except as permitted by 250.34 for portable and vehicle-mounted generators, the grounding elec‐ trode shall comply with 250.30(A)(4).
3. Bonding Path and Conductor. A supply-side bonding jumper shall be installed from the source of a separately derived system to the first disconnecting means in compliance with 250.30(A)(2).
Outdoor Source. If the source of the separately derived system is located outside the building or structure supplied, a grounding electrode connection shall be made at the source location to one or more grounding electrodes in compliance with 250.50. In addition, the installation shall comply with 250.30(A) for grounded systems or with 250.30(B) for ungrounded systems.

Exception: The grounding electrode conductor connection for impedance grounded neutral systems shall comply with 250.36 or 250.187, as applicable.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).

Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a ground‐ ing electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding elec‐ trode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding elec‐ trode, the grounding electrode(s) required in 250.50 shall be installed.Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non–current-carrying metal parts of equipment.
Grounded Systems.
1. Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding elec‐ trode(s). The equipment grounding conductor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment ground‐ ing conductor shall be sized in accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding elec‐ trode(s).Exception No. 1: For installations made in compliance with previous editions of this Code that permitted such connection, the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path if all of the following requirements continue to be met:
  1. An equipment grounding conductor is not run with the supply to the building or structure.
  2. There are no continuous metallic paths bonded to the grounding system in each building or structure involved.
  3. Ground-fault protection of equipment has not been installed on the supply side of the feeder(s).
  If the grounded conductor is used for grounding in accordance with the provision of this exception, the size of the grounded conductor shall not be smaller than the larger of either of the following:
  1. That required by 220.61
  2. That required by 250.122Exception No. 2: If system bonding jumpers are installed in accordance with 250.30(A)(1), Exception No. 2, the feeder grounded circuit conductor at the building or structure served shall be connected to the equipment grounding conductors, grounding electrode conductor, and the enclosure for the first disconnecting means.
    1. Supplied by Separately Derived System.
      1. With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with 250.32(B)(1).
      2. Without Overcurrent Protection. If overcurrent protec‐ tion is not provided where the conductors originate, the instal‐ lation shall comply with 250.30(A). If installed, the supply-side bonding jumper shall be connected to the building or struc‐ ture disconnecting means and to the grounding electrode(s).
Ungrounded Systems.
1. Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, shall be instal‐ led with the supply conductors and be connected to the build‐ ing or structure disconnecting means and to the grounding electrode(s). The grounding electrode(s) shall also be connec‐ ted to the building or structure disconnecting means.
2. Supplied by a Separately Derived System.
  1. With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the installation shall comply with (C)(1).
  2. Without Overcurrent Protection. If overcurrent protec‐ tion is not provided where the conductors originate, the instal‐ lation shall comply with 250.30(B). If installed, the supply-side bonding jumper shall be connected to the building or struc‐ ture disconnecting means and to the grounding electrode(s).
Disconnecting Means Located in Separate Building or Structure on the Same Premises. Where one or more discon‐ necting means supply one or more additional buildings or structures under single management, and where these discon‐ necting means are located remote from those buildings or structures in accordance with the provisions of 225.32, Excep‐ tion No. 1 and No. 2, 700.12(B)(6), 701.12(B)(5), or 702.12, all of the following conditions shall be met:
1. The connection of the grounded conductor to the grounding electrode, to normally non–current-carrying metal parts of equipment, or to the equipment ground‐ ing conductor at a separate building or structure shall not be made.
2. An equipment grounding conductor for grounding and bonding any normally non–current-carrying metal parts of equipment, interior metal piping systems, and building or structural metal frames is run with the circuit conduc‐ tors to a separate building or structure and connected to existing grounding electrode(s) required in Part III of this article, or, where there are no existing electrodes, the grounding electrode(s) required in Part III of this article shall be installed where a separate building or structure is supplied by more than one branch circuit.
3. The connection between the equipment grounding conductor and the grounding electrode at a separate building or structure shall be made in a junction box, panelboard, or similar enclosure located immediately inside or outside the separate building or structure.
Grounding Electrode Conductor. The size of the ground‐ ing electrode conductor to the grounding electrode(s) shall not be smaller than given in 250.66, based on the largest ungrounded supply conductor. The installation shall comply with Part III of this article.

Portable and Vehicle-Mounted Generators.
1. Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
  1. The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
  2. The normally non–current-carrying metal parts of equip‐ ment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.
2. Vehicle-Mounted Generators. The frame of a vehicle shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle under the following conditions:
  1. The frame of the generator is bonded to the vehicle frame, and
  2. The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
  3. The normally non–current-carrying metal parts of equip‐ ment and the equipment grounding conductor terminals of the receptacles are connected to the generator frame.
3. Grounded Conductor Bonding. A system conductor that is required to be grounded by 250.26 shall be connected to the generator frame where the generator is a component of a sepa‐ rately derived system.
Informational Note: For grounding portable generators supply‐ ing fixed wiring systems, see 250.30.
Permanently Installed Generators. A conductor that provides an effective ground-fault current path shall be instal‐ led with the supply conductors from a permanently installed generator(s) to the first disconnecting mean(s) in accordance with (A) or (B).
1. Separately Derived System. If the generator is installed as a separately derived system, the requirements in 250.30 shall apply.
2. Nonseparately Derived System. If the generator is instal‐ led as a nonseparately derived system, and overcurrent protec‐ tion is not integral with the generator assembly, a supply-side bonding jumper shall be installed between the generator equipment grounding terminal and the equipment grounding terminal, bar, or bus of the disconnecting mean(s). It shall be sized in accordance with 250.102(C) based on the size of the conductors supplied by the generator.
High-Impedance Grounded Neutral Systems. High- impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current to a low value shall be permitted for 3-phase ac systems of 480 volts to 1000 volts if all the following conditions are met:

The conditions of maintenance and supervision ensure that only qualified persons service the installation.
Ground detectors are installed on the system.
Line-to-neutral loads are not served.
High-impedance grounded neutral systems shall comply with the provisions of 250.36(A) through (G).
1. Location. The grounding impedance shall be installed between the grounding electrode conductor and the system neutral point. If a neutral point is not available, the grounding impedance shall be installed between the grounding electrode conductor and the neutral point derived from a grounding transformer.
2. Conductor Insulation and Ampacity. The grounded system conductor from the neutral point of the transformer or generator to its connection point to the grounding impedance shall be fully insulated.The grounded system conductor shall have an ampacity of not less than the maximum current rating of the grounding impedance but in no case shall the grounded system conductor be smaller than 8 AWG copper or 6 AWG aluminum or copper- clad aluminum.
3. System Grounding Connection. The system shall not be connected to ground except through the grounding impe‐ dance.Informational Note: The impedance is normally selected to limit the ground-fault current to a value slightly greater than or equal to the capacitive charging current of the system. This value of impedance will also limit transient overvoltages to safe values. For guidance, refer to criteria for limiting transient overvoltages in ANSI/IEEE 142-2007, Recommended Practice for Grounding of Industrial and Commercial Power Systems.
4. Conductor Routing. The conductor connecting the neutral point of the transformer or generator to the grounding impedance shall be permitted to be installed in a separate race‐ way from the ungrounded conductors. It shall not be required to run this conductor with the phase conductors to the first system disconnecting means or overcurrent device.
5. Equipment Bonding Jumper. The equipment bonding jumper (the connection between the equipment grounding conductors and the grounding impedance) shall be an unspliced conductor run from the first system disconnecting means or overcurrent device to the grounded side of the grounding impedance.
6. Grounding Electrode Conductor Connection Location. For services or separately derived systems, the grounding elec‐ trode conductor shall be connected at any point from the grounded side of the grounding impedance to the equipment grounding connection at the service equipment or the first system disconnecting means of a separately derived system.
7. Equipment Bonding Jumper Size. The equipment bond‐ ing jumper shall be sized in accordance with (1) or (2) as follows:

If the grounding electrode conductor connection is made at the grounding impedance, the equipment bonding jumper shall be sized in accordance with 250.66, based on the size of the service entrance conductors for a service or the derived phase conductors for a separately derived system.
If the grounding electrode conductor is connected at the first system disconnecting means or overcurrent device, the equipment bonding jumper shall be sized the same as the neutral conductor in 250.36(B).

Part III. Grounding Electrode System and Grounding Elec‐ trode Conductor

250.50 Grounding Electrode System. All grounding electro‐ des as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.

Exception: Concrete-encased electrodes of existing buildings or structures shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods are not accessible for use without disturbing the concrete.

250.52 Grounding Electrodes.

Electrodes Permitted for Grounding.
1. Metal Underground Water Pipe. A metal underground water pipe in direct contact with the earth for 3.0 m (10 ft) or more (including any metal well casing bonded to the pipe) and electrically continuous (or made electrically continuous by bonding around insulating joints or insulating pipe) to the points of connection of the grounding electrode conductor and the bonding conductor(s) or jumper(s), if installed.N
2. Metal In-ground Support Structure(s). One or more metal in-ground support structure(s) in direct contact with the earth vertically for 3.0 m (10 ft) or more, with or without concrete encasement. If multiple metal in-ground support structures are present at a building or a structure, it shall be permissible to bond only one into the grounding electrode system.
  Informational Note: Metal in-ground support structures include, but are not limited to, pilings, casings, and other structural metal.
3. Concrete-Encased Electrode. A concrete-encased elec‐ trode shall consist of at least 6.0 m (20 ft) of either (1) or (2):
  1. One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (1∕2 in.) in diameter, installed in one continuous 6.0 m (20 ft) length, or if in multiple pieces connected together by the usual steel tie wires, exother‐ mic welding, welding, or other effective means to create a6.0 m (20 ft) or greater length; or
  2. Bare copper conductor not smaller than 4 AWG
  Metallic components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or struc‐ tural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.Informational Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in “direct contact” with the earth.
  1. Ground Ring. A ground ring encircling the building or structure, in direct contact with the earth, consisting of at least6.0 m (20 ft) of bare copper conductor not smaller than 2 AWG.
  2. Rod and Pipe Electrodes. Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in length and shall consist of the following materials.
    1. Grounding electrodes of pipe or conduit shall not be smaller than metric designator 21 (trade size 3∕4) and, where of steel, shall have the outer surface galvanized or otherwise metal-coated for corrosion protection.
    2. Rod-type grounding electrodes of stainless steel and copper or zinc coated steel shall be at least 15.87 mm (5∕8 in.) in diameter, unless listed.
  3. Other Listed Electrodes. Other listed grounding electro‐ des shall be permitted.
  4. Plate Electrodes. Each plate electrode shall expose not less than 0.186 m2 (2 ft2) of surface to exterior soil. Electrodes of bare or electrically conductive coated iron or steel plates shall be at least 6.4 mm (1∕4 in.) in thickness. Solid, uncoated electrodes of nonferrous metal shall be at least 1.5 mm (0.06 in.) in thickness.
  5. Other Local Metal Underground Systems or Structures. Other local metal underground systems or structures such as piping systems, underground tanks, and underground metal well casings that are not bonded to a metal water pipe.
Not Permitted for Use as Grounding Electrodes. The following systems and materials shall not be used as grounding electrodes:

Metal underground gas piping systems
Aluminum

(3) The structures and structural reinforcing steel described

in 680.26(B)(1) and (B)(2)

Informational Note: See 250.104(B) for bonding requirements of gas piping.

Grounding Electrode System Installation.
1. Rod, Pipe, and Plate Electrodes. Rod, pipe, and plate electrodes shall meet the requirements of 250.53(A)(1) through (A)(3).
  1. Below Permanent Moisture Level. If practicable, rod, pipe, and plate electrodes shall be embedded below permanent moisture level. Rod, pipe, and plate electrodes shall be free from nonconductive coatings such as paint or enamel.
  2. Supplemental Electrode Required. A single rod, pipe, or plate electrode shall be supplemented by an additional elec‐ trode of a type specified in 250.52(A)(2) through (A)(8). The supplemental electrode shall be permitted to be bonded to one of the following:
    1. Rod, pipe, or plate electrode
    2. Grounding electrode conductor
    3. Grounded service-entrance conductor
    4. Nonflexible grounded service raceway
    5. Any grounded service enclosure
    Exception: If a single rod, pipe, or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required.(3) Supplemental Electrode. If multiple rod, pipe, or plate electrodes are installed to meet the requirements of this section, they shall not be less than 1.8 m (6 ft) apart.Informational Note: The paralleling efficiency of rods is increased by spacing them twice the length of the longest rod.
2. Electrode Spacing. Where more than one of the electro‐ des of the type specified in 250.52(A)(5) or (A)(7) are used, each electrode of one grounding system (including that used for strike termination devices) shall not be less than 1.83 m (6 ft) from any other electrode of another grounding system. Two or more grounding electrodes that are bonded together shall be considered a single grounding electrode system.
3. Bonding Jumper. The bonding jumper(s) used to connect the grounding electrodes together to form the grounding electrode system shall be installed in accordance with 250.64(A), (B), and (E), shall be sized in accordance with 250.66, and shall be connected in the manner specified in 250.70.
4. Metal Underground Water Pipe. If used as a grounding electrode, metal underground water pipe shall meet the requirements of 250.53(D)(1) and (D)(2).
  1. Continuity. Continuity of the grounding path or the bond‐ ing connection to interior piping shall not rely on water meters or filtering devices and similar equipment.
  2. Supplemental Electrode Required. A metal underground water pipe shall be supplemented by an additional electrode of a type specified in 250.52(A)(2) through (A)(8). If the supple‐ mental electrode is of the rod, pipe, or plate type, it shall comply with 250.53(A). The supplemental electrode shall be bonded to one of the following:
    1. Grounding electrode conductor
    2. Grounded service-entrance conductor
    3. Nonflexible grounded service raceway
    4. Any grounded service enclosure
    5. As provided by 250.32(B)
    Exception: The supplemental electrode shall be permitted to be bonded to the interior metal water piping at any convenient point as specified in 250.68(C)(1), Exception.
5. Supplemental Electrode Bonding Connection Size. Where the supplemental electrode is a rod, pipe, or plate electrode, that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
6. Ground Ring. The ground ring shall be installed not less than 750 mm (30 in.) below the surface of the earth.
7. Rod and Pipe Electrodes. The electrode shall be installed such that at least 2.44 m (8 ft) of length is in contact with the soil. It shall be driven to a depth of not less than 2.44 m (8 ft) except that, where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the vertical or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be buried in a trench that is at least 750 mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the aboveground end and the grounding electrode conductor attachment are protected against physical damage as specified in 250.10.
8. Plate Electrode. Plate electrodes shall be installed not less than 750 mm (30 in.) below the surface of the earth.
Auxiliary Grounding Electrodes. One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding

requirements of 250.50 or 250.53(C) or the resistance require‐ ments of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4).

250.58 Common Grounding Electrode. Where an ac system is connected to a grounding electrode in or at a building or struc‐ ture, the same electrode shall be used to ground conductor enclosures and equipment in or on that building or structure. Where separate services, feeders, or branch circuits supply a building and are required to be connected to a grounding elec‐ trode(s), the same grounding electrode(s) shall be used.

Two or more grounding electrodes that are bonded together shall be considered as a single grounding electrode system in this sense.

250.60 Use of Strike Termination Devices. Conductors and driven pipes, rods, or plate electrodes used for grounding strike termination devices shall not be used in lieu of the grounding electrodes required by 250.50 for grounding wiring systems and equipment. This provision shall not prohibit the required bonding together of grounding electrodes of differ‐ ent systems.

Informational Note No. 1: See 250.106 for the bonding require‐ ment of the lightning protection system components to the building or structure grounding electrode system.

Informational Note No. 2: Bonding together of all separate grounding electrodes will limit voltage differences between them and between their associated wiring systems.

250.62 Grounding Electrode Conductor Material. The grounding electrode conductor shall be of copper, aluminum, copper-clad aluminum, or the items as permitted in 250.68(C). The material selected shall be resistant to any corrosive condi‐ tion existing at the installation or shall be protected against corrosion. Conductors of the wire type shall be solid or stran‐ ded, insulated, covered, or bare.

250.64 Grounding Electrode Conductor Installation. Ground‐ ing electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F).

Aluminum or Copper-Clad Aluminum Conductors. Bare aluminum or copper-clad aluminum grounding electrode conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within 450 mm (18 in.) of the earth.
Securing and Protection Against Physical Damage. Where exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried. Grounding electrode conductors shall be permitted to be installed on or through framing members.
1. Not Exposed to Physical Damage. A 6 AWG or larger copper or aluminum grounding electrode conductor not exposed to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection.
2. Exposed to Physical Damage. A 6 AWG or larger copper or aluminum grounding electrode conductor exposed to physi‐ cal damage shall be protected in rigid metal conduit (RMC),intermediate metal conduit (IMC), rigid polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit Type XW (RTRC-XW), electrical metallic tubing (EMT), or cable armor.
3. Smaller Than 6 AWG. Grounding electrode conductors smaller than 6 AWG shall be protected in RMC, IMC, PVC, RTRC-XW, EMT, or cable armor.
4. In Contact with the Earth. Grounding electrode conduc‐ tors and grounding electrode bonding jumpers in contact with the earth shall not be required to comply with 300.5, but shall be buried or otherwise protected if subject to physical damage.
Continuous. Except as provided in 250.30(A)(5) and (A)(6), 250.30(B)(1), and 250.68(C), grounding electrode conductor(s) shall be installed in one continuous length with‐ out a splice or joint. If necessary, splices or connections shall be made as permitted in (1) through (4):
1. Splicing of the wire-type grounding electrode conductor shall be permitted only by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process.
2. Sections of busbars shall be permitted to be connected together to form a grounding electrode conductor.
3. Bolted, riveted, or welded connections of structural metal frames of buildings or structures.
4. Threaded, welded, brazed, soldered or bolted-flange connections of metal water piping.
Building or Structure with Multiple Disconnecting Means in Separate Enclosures. If a building or structure is supplied by a service or feeder with two or more disconnecting means in separate enclosures, the grounding electrode connections shall be made in accordance with 250.64(D)(1),250.64(D)(2), or 250.64(D)(3).
1. Common Grounding Electrode Conductor and Taps. A common grounding electrode conductor and grounding elec‐ trode conductor taps shall be installed. The common ground‐ ing electrode conductor shall be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded conductor(s) of each set of conductors that supplies the disconnecting means. If the service-entrance conductors connect directly to the overhead service conduc‐ tors, service drop, underground service conductors, or service lateral, the common grounding electrode conductor shall be sized in accordance with Table 250.66, note 1.A grounding electrode conductor tap shall extend to the inside of each disconnecting means enclosure. The grounding electrode conductor taps shall be sized in accordance with250.66 for the largest service-entrance or feeder conductor serving the individual enclosure. The tap conductors shall be connected to the common grounding electrode conductor by one of the following methods in such a manner that the common grounding electrode conductor remains without a splice or joint:
  1. Exothermic welding.
  2. Connectors listed as grounding and bonding equipment.
  3. Connections to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1∕4 in. thick × 2 in. wide) and of sufficient length to accommodate the number of terminations necessary for the installation. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed
  connector or by the exothermic welding process. If alumi‐ num busbars are used, the installation shall comply with 250.64(A).(2) Individual Grounding Electrode Conductors. A ground‐ ing electrode conductor shall be connected between the grounding electrode system and one or more of the following, as applicable:
  1. Grounded conductor in each service equipment discon‐ necting means enclosure
  2. Equipment grounding conductor installed with the feeder
  3. Supply-side bonding jumper
  Each grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance or feeder conductor(s) supplying the individual disconnecting means.(3) Common Location. A grounding electrode conductor shall be connected in a wireway or other accessible enclosure on the supply side of the disconnecting means to one or more of the following, as applicable:
  1. Grounded service conductor(s)
  2. Equipment grounding conductor installed with the feeder
  3. Supply-side bonding jumper
  The connection shall be made with exothermic welding or a connector listed as grounding and bonding equipment. The grounding electrode conductor shall be sized in accordance with 250.66 based on the service-entrance or feeder conduc‐ tor(s) at the common location where the connection is made.
Raceways and Enclosures for Grounding Electrode Conductors.
1. General. Ferrous metal raceways and enclosures for grounding electrode conductors shall be electrically continu‐ ous from the point of attachment to cabinets or equipment to the grounding electrode and shall be securely fastened to the ground clamp or fitting. Ferrous metal raceways and enclosures shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create an electrically parallel path. Nonferrous metal raceways and enclosures shall not be required to be electrically continu‐ ous.
2. Methods. Bonding shall be in compliance with 250.92(B) and ensured by one of the methods in 250.92(B)(2) through (B)(4).
3. Size. The bonding jumper for a grounding electrode conductor raceway or cable armor shall be the same size as, or larger than, the enclosed grounding electrode conductor.
4. Wiring Methods. If a raceway is used as protection for a grounding electrode conductor, the installation shall comply with the requirements of the appropriate raceway article.
Installation to Electrode(s). Grounding electrode conduc‐ tor(s) and bonding jumpers interconnecting grounding elec‐ trodes shall be installed in accordance with (1), (2), or (3). The grounding electrode conductor shall be sized for the larg‐ est grounding electrode conductor required among all the electrodes connected to it.

The grounding electrode conductor shall be permitted to be run to any convenient grounding electrode availablein the grounding electrode system where the other elec‐ trode(s), if any, is connected by bonding jumpers that are installed in accordance with 250.53(C).
Grounding electrode conductor(s) shall be permitted to be run to one or more grounding electrode(s) individu‐ ally.
Bonding jumper(s) from grounding electrode(s) shall be permitted to be connected to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1∕4 in. thick × 2 in wide.) and of sufficient length to accommo‐ date the number of terminations necessary for the instal‐ lation. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector or by the exothermic welding process. The grounding electrode conductor shall be permitted to be run to the busbar. Where aluminum busbars are used, the installation shall comply with 250.64(A).

250.66 Size of Alternating-Current Grounding Electrode Conductor. The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).

Connections to a Rod, Pipe, or Plate Electrode(s). If the grounding electrode conductor or bonding jumper connected to a single or multiple rod, pipe, or plate electrode(s), or any combination thereof, as described in 250.52(A)(5) or (A)(7), does not extend on to other types of electrodes that require a larger size conductor, the grounding electrode conductor shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
Connections to Concrete-Encased Electrodes. If the grounding electrode conductor or bonding jumper connected to a single or multiple concrete-encased electrode(s), as descri‐ bed in 250.52(A)(3), does not extend on to other types of elec‐ trodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than 4 AWG copper wire.
Connections to Ground Rings. If the grounding electrode conductor or bonding jumper connected to a ground ring, as described in 250.52(A)(4), does not extend on to other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than the conductor used for the ground ring.

250.68 Grounding Electrode Conductor and Bonding Jumper Connection to Grounding Electrodes. The connection of a grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system and associated bonding jumper(s) shall be made as specified 250.68(A) through (C).

Accessibility. All mechanical elements used to terminate a grounding electrode conductor or bonding jumper to a grounding electrode shall be accessible.Exception No. 1: An encased or buried connection to a concrete-encased, driven, or buried grounding electrode shall not be required to be accessi‐ ble.Exception No. 2: Exothermic or irreversible compression connections used at terminations, together with the mechanical means used to
attach such terminations to fireproofed structural metal whether or not the mechanical means is reversible, shall not be required to be accessible.
Effective Grounding Path. The connection of a ground‐ ing electrode conductor or bonding jumper to a grounding electrode shall be made in a manner that will ensure an effec‐ tive grounding path. Where necessary to ensure the grounding path for a metal piping system used as a grounding electrode, bonding shall be provided around insulated joints and around any equipment likely to be disconnected for repairs or replace‐ ment. Bonding jumpers shall be of sufficient length to permit removal of such equipment while retaining the integrity of the grounding path.
Grounding Electrode Conductor Connections. Ground‐ ing electrode conductors and bonding jumpers shall be permit‐ ted to be connected at the following locations and used to extend the connection to an electrode(s):

Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall not be used as a conductor
Table 250.66 Grounding Electrode Conductor for Alternating- Current Systems
Size of Largest Ungrounded Service-to interconnect electrodes of the grounding electrode system.Exception: In industrial, commercial, and institutional buildings or structures, if conditions of maintenance and supervision ensure that only qualified persons service the installation, interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building shall be permitted as a bonding conductor to interconnect elec‐ trodes that are part of the grounding electrode system, or as a grounding electrode conductor, if the entire length, other than short sections pass‐ ing perpendicularly through walls, floors, or ceilings, of the interior metal water pipe that is being used for the conductor is exposed.
The metal structural frame of a building shall be permit‐ ted to be used as a conductor to interconnect electrodes that are part of the grounding electrode system, or as a grounding electrode conductor. Hold-down bolts secur‐ing the structural steel column that are connected to aconcrete-encased electrode that complies with 250.52(A)(3) and is located in the support footing or foundation shall be permitted to connect the metal struc‐ tural frame of a building or structure to the concrete encased grounding electrode. The hold-down bolts shall be connected to the concrete-encased electrode by weld‐ ing, exothermic welding, the usual steel tie wires, or otherapproved means.
A rebar-type concrete-encased electrode installed in accordance with 250.52(A)(3) with an additional rebar section extended from its location within the concrete to an accessible location that is not subject to corrosion shall be permitted for connection of grounding electrode conductors and bonding jumpers. The rebar extension

Entrance Conductor or Equivalent Area for Parallel Conductorsa

Notes:

Size of Grounding Electrode Conductor

shall not be exposed to contact with the earth without corrosion protection.

(AWG/kcmil) (AWG/kcmil)
	Aluminum or		Aluminum or
	Copper-Clad		Copper-Clad
Copper	Aluminum	Copper	Aluminumb
2 or smaller	1/0 or smaller	8	6
1 or 1/0	2/0 or 3/0	6	4
2/0 or 3/0	4/0 or 250	4	2
Over 3/0 through 350	Over 250through 500	2	1/0
Over 350	Over 500	1/0	3/0
through 600	through 900
Over 600through 1100	Over 900through 1750	2/0	4/0
Over 1100	Over 1750	3/0	250

250.70 Methods of Grounding and Bonding Conductor Connection to Electrodes. The grounding or bonding conductor shall be connected to the grounding electrode by exothermic welding, listed lugs, listed pressure connectors, listed clamps, or other listed means. Connections depending on solder shall not be used. Ground clamps shall be listed for the materials of the grounding electrode and the grounding electrode conductor and, where used on pipe, rod, or other buried electrodes, shall also be listed for direct soil burial or concrete encasement. Not more than one conductor shall be connected to the grounding electrode by a single clamp or fitting unless the clamp or fitting is listed for multiple conduc‐ tors. One of the following methods shall be used:

A pipe fitting, pipe plug, or other approved device screwed into a pipe or pipe fitting
A listed bolted clamp of cast bronze or brass, or plain or malleable iron
For indoor communications purposes only, a listed sheet metal strap-type ground clamp having a rigid metal base
1. If multiple sets of service-entrance conductors connect directly to a service drop, set of overhead service conductors, set of underground service conductors, or service lateral, the equivalent size of the largest service-entrance conductor shall be determined by the largest sum of the areas of the corresponding conductors of each set.
2. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.
aThis table also applies to the derived conductors of separately derived ac systems.bSee installation restrictions in 250.64(A).that seats on the electrode and having a strap of such material and dimensions that it is not likely to stretch during or after installation
An equally substantial approved means

Part IV. Enclosure, Raceway, and Service Cable Connections

250.80 Service Raceways and Enclosures. Metal enclosures and raceways for service conductors and equipment shall be connected to the grounded system conductor if the electrical

system is grounded or to the grounding electrode conductor for electrical systems that are not grounded.

Exception: Metal components that are installed in a run of under‐ ground nonmetallic raceway(s) and are isolated from possible contact by a minimum cover of 450 mm (18 in.) to all parts of the metal compo‐ nents shall not be required to be connected to the grounded system conductor, supply side bonding jumper, or grounding electrode conduc‐ tor.

250.84 Underground Service Cable or Raceway.

Underground Service Cable. The sheath or armor of a continuous underground metal-sheathed or armored service cable system that is connected to the grounded system conduc‐ tor on the supply side shall not be required to be connected to the grounded system conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping.
Underground Service Raceway Containing Cable. An underground metal service raceway that contains a metal- sheathed or armored cable connected to the grounded system conductor shall not be required to be connected to the groun‐ ded system conductor at the building or structure. The sheath or armor shall be permitted to be insulated from the interior metal raceway or piping.

250.86 Other Conductor Enclosures and Raceways. Except as permitted by 250.112(I), metal enclosures and raceways for other than service conductors shall be connected to the equip‐ ment grounding conductor.

Exception No. 1: Metal enclosures and raceways for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallic-sheathed cable shall not be required to be connected to the equipment grounding conductor where these enclosures or wiring meth‐ ods comply with (1) through (4) as follows:

Do not provide an equipment ground
Are in runs of less than 7.5 m (25 ft)
Are free from probable contact with ground, grounded metal, metal lath, or other conductive material
Are guarded against contact by persons

Exception No. 2: Short sections of metal enclosures or raceways used to provide support or protection of cable assemblies from physical damage shall not be required to be connected to the equipment grounding conductor.

Exception No. 3: Metal components shall not be required to be connec‐ ted to the equipment grounding conductor or supply-side bonding jumper where either of the following conditions exist:

The metal components are installed in a run of nonmetallic race‐ way(s) and isolated from possible contact by a minimum cover of 450 mm (18 in.) to any part of the metal components.
The metal components are part of an installation of nonmetallic raceway(s) and are isolated from possible contact to any part of the metal components by being encased in not less than 50 mm (2 in.) of concrete.

Part V. Bonding

250.90 General. Bonding shall be provided where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed.

250.92 Services.

Bonding of Equipment for Services. The normally non– current-carrying metal parts of equipment indicated in 250.92(A)(1) and (A)(2) shall be bonded together.
1. All raceways, cable trays, cablebus framework, auxiliary gutters, or service cable armor or sheath that enclose, contain, or support service conductors, except as permit‐ ted in 250.80
2. All enclosures containing service conductors, including meter fittings, boxes, or the like, interposed in the service raceway or armor
Method of Bonding at the Service. Bonding jumpers meeting the requirements of this article shall be used around impaired connections, such as reducing washers or oversized, concentric, or eccentric knockouts. Standard locknuts or bush‐ ings shall not be the only means for the bonding required by this section but shall be permitted to be installed to make a mechanical connection of the raceway(s).

Electrical continuity at service equipment, service raceways, and service conductor enclosures shall be ensured by one of the following methods:

Bonding equipment to the grounded service conductor in a manner provided in 250.8
Connections utilizing threaded couplings or threaded hubs on enclosures if made up wrenchtight
Threadless couplings and connectors if made up tight for metal raceways and metal-clad cables
Other listed devices, such as bonding-type locknuts, bush‐ ings, or bushings with bonding jumpers

250.94 Bonding for Communication Systems. Communica‐ tions system bonding terminations shall be connected in accordance with (A) or (B).

The Intersystem Bonding Termination Device. An inter‐ system bonding termination (IBT) for connecting intersystem bonding conductors shall be provided external to enclosures at the service equipment or metering equipment enclosure and at the disconnecting means for any additional buildings or struc‐ tures. If an IBT is used, it shall comply with the following:
1. Be accessible for connection and inspection.
2. Consist of a set of terminals with the capacity for connec‐ tion of not less than three intersystem bonding conduc‐ tors.
3. Not interfere with opening the enclosure for a service, building or structure disconnecting means, or metering equipment.
4. At the service equipment, be securely mounted and elec‐ trically connected to an enclosure for the service equip‐ ment, to the meter enclosure, or to an exposed nonflexible metallic service raceway, or be mounted at one of these enclosures and be connected to the enclo‐ sure or to the grounding electrode conductor with a minimum 6 AWG copper conductor.
5. At the disconnecting means for a building or structure, be securely mounted and electrically connected to the metallic enclosure for the building or structure discon‐ necting means, or be mounted at the disconnecting means and be connected to the metallic enclosure or to the grounding electrode conductor with a minimum 6 AWG copper conductor.
6. The terminals shall be listed as grounding and bonding equipment.
Exception: In existing buildings or structures where any of the intersys‐ tem bonding and grounding electrode conductors required by 770.100(B)(2), 800.100(B)(2), 810.21(F)(2), 820.100(B)(2), and830.100(B)(2) exist, installation of the intersystem bonding termina‐ tion is not required. An accessible means external to enclosures for connecting intersystem bonding and grounding electrode conductors shall be permitted at the service equipment and at the disconnecting means for any additional buildings or structures by at least one of the following means:
1. Exposed nonflexible metallic raceways
2. An exposed grounding electrode conductor
3. Approved means for the external connection of a copper or other corrosion-resistant bonding or grounding electrode conductor to the grounded raceway or equipment
Informational Note No. 1: A 6 AWG copper conductor with one end bonded to the grounded nonflexible metallic raceway or equipment and with 150 mm (6 in.) or more of the other end made accessible on the outside wall is an example of the approved means covered in 250.94, Exception item (3).Informational Note No. 2: See 770.100, 800.100, 810.21, 820.100, and 830.100 for intersystem bonding and grounding requirements for conductive optical fiber cables, communica‐ tions circuits, radio and television equipment, CATV circuits and network-powered broadband communications systems, respec‐ tively.N
Other Means. Connections to an aluminum or copper busbar not less than 6 mm thick × 50 mm wide (1∕4 in. thick × 2 in. wide) and of sufficient length to accommodate at least three terminations for communication systems in addition to other connections. The busbar shall be securely fastened and shall be installed in an accessible location. Connections shall be made by a listed connector. If aluminum busbars are used, the installation shall also comply with 250.64(A).

Exception to (A) and (B): Means for connecting intersystem bonding conductors are not required where communications systems are not likely to be used.

Informational Note: The use of an IBT can reduce electrical noise on communication systems.

Bonding Other Enclosures.
1. General. Metal raceways, cable trays, cable armor, cable sheath, enclosures, frames, fittings, and other metal non– current-carrying parts that are to serve as equipment ground‐ ing conductors, with or without the use of supplementary equipment grounding conductors, shall be bonded where necessary to ensure electrical continuity and the capacity to conduct safely any fault current likely to be imposed on them. Any nonconductive paint, enamel, or similar coating shall be removed at threads, contact points, and contact surfaces or shall be connected by means of fittings designed so as to make such removal unnecessary.
2. Isolated Grounding Circuits. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, an equipment enclosure supplied by a branch circuit shall be permitted to be isolated from a raceway containing circuits supplying only that equipment by one or more listed nonmetallic raceway fittings located at the point of attachment of the raceway to the equipment enclosure. The metal raceway shall comply with provisions of this article and
shall be supplemented by an internal insulated equipment grounding conductor installed in accordance with 250.146(D) to ground the equipment enclosure.Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system.
Bonding for Over 250 Volts. For circuits of over 250 volts to ground, the electrical continuity of metal raceways and cables with metal sheaths that contain any conductor other than service conductors shall be ensured by one or more of the methods specified for services in 250.92(B), except for (B)(1).Exception: Where oversized, concentric, or eccentric knockouts are not encountered, or where a box or enclosure with concentric or eccentric knockouts is listed to provide a reliable bonding connection, the follow‐ ing methods shall be permitted:
1. Threadless couplings and connectors for cables with metal sheaths
2. Two locknuts, on rigid metal conduit or intermediate metal conduit, one inside and one outside of boxes and cabinets
3. Fittings with shoulders that seat firmly against the box or cabinet, such as electrical metallic tubing connectors, flexible metal conduit connectors, and cable connectors, with one locknut on the inside of boxes and cabinets
4. Listed fittings
Bonding Loosely Jointed Metal Raceways. Expansion fittings and telescoping sections of metal raceways shall be made electrically continuous by equipment bonding jumpers or other means.

250.100 Bonding in Hazardous (Classified) Locations. Regardless of the voltage of the electrical system, the electrical continuity of non–current-carrying metal parts of equipment, raceways, and other enclosures in any hazardous (classified) location, as defined in 500.5, 505.5, and 506.5, shall be ensured by any of the bonding methods specified in 250.92(B)(2) through (B)(4). One or more of these bonding methods shall be used whether or not equipment grounding conductors of the wire type are installed.

Informational Note: See 501.30, 502.30, 503.30, 505.25, or

506.25 for specific bonding requirements.

250.102 Grounded Conductor, Bonding Conductors, and Jumpers.

Material. Bonding jumpers shall be of copper, aluminum, copper-clad aluminum, or other corrosion-resistant material. A bonding jumper shall be a wire, bus, screw, or similar suitable conductor.
Attachment. Bonding jumpers shall be attached in the manner specified by the applicable provisions of 250.8 for circuits and equipment and by 250.70 for grounding electro‐ des.
Size — Supply-Side Bonding Jumper.
1. Size for Supply Conductors in a Single Raceway or Cable. The supply-side bonding jumper shall not be smaller than specified in Table 250.102(C)(1).
2. Size for Parallel Conductor Installations in Two or More Raceways or Cables. Where the ungrounded supply conduc‐ tors are paralleled in two or more raceways or cables, and an individual supply-side bonding jumper is used for bonding these raceways or cables, the size of the supply-side bonding
  jumper for each raceway or cable shall be selected from Table 250.102(C)(1) based on the size of the ungrounded supply conductors in each raceway or cable. A single supply-side bond‐Table 250.102(C)(1) Grounded Conductor, Main Bonding Jumper, System Bonding Jumper, and Supply-Side Bonding Jumper for Alternating-Current Systemsing jumper installed for bonding two or more raceways or cables shall be sized in accordance with 250.102(C)(1).Informational Note No. 1: The term supply conductors includes ungrounded conductors that do not have overcurrent protec‐ tion on their supply side and terminate at service equipment or the first disconnecting means of a separately derived system.Size of Largest Ungrounded Conductor or Equivalent Area for Parallel Conductors (AWG/kcmil)Aluminum or Copper-Clad
  Size of Grounded Conductor or Bonding Jumper* (AWG/kcmil)Aluminum or Copper-CladInformational Note No. 2: See Chapter 9, Table 8, for the circu‐lar mil area of conductors 18 AWG through 4/0 AWG.CopperAluminum CopperAluminum
Size — Equipment Bonding Jumper on Load Side of an Overcurrent Device. The equipment bonding jumper on the2 or smaller 1/0 or smaller 8 61 or 1/0 2/0 or 3/0 6 42/0 or 3/04/0 or 25042Over 3/0 through 350Over 250through 50021/0Over 350through 600Over 500through 9001/03/0Over 600 through 1100Over 900 through 17502/04/0load side of an overcurrent device(s) shall be sized in accord‐ ance with 250.122.A single common continuous equipment bonding jumper shall be permitted to connect two or more raceways or cables if the bonding jumper is sized in accordance with 250.122 for the largest overcurrent device supplying circuits therein.
Installation. Bonding jumpers or conductors and equip‐ ment bonding jumpers shall be permitted to be installed inside or outside of a raceway or an enclosure.
1. Inside a Raceway or an Enclosure. If installed inside a raceway, equipment bonding jumpers and bonding jumpers or conductors shall comply with the requirements of 250.119 and 250.148.
2. Outside a Raceway or an Enclosure. If installed on the outside, the length of the bonding jumper or conductor or equipment bonding jumper shall not exceed 1.8 m (6 ft) and shall be routed with the raceway or enclosure.Exception: An equipment bonding jumper or supply-side bonding jumper longer than 1.8 m (6 ft) shall be permitted at outside pole loca‐ tions for the purpose of bonding or grounding isolated sections of metal raceways or elbows installed in exposed risers of metal conduit or other metal raceway, and for bonding grounding electrodes, and shall not be required to be routed with a raceway or enclosure.
3. Protection. Bonding jumpers or conductors and equip‐ ment bonding jumpers shall be installed in accordance with 250.64(A) and (B).

250.104 Bonding of Piping Systems and Exposed Structural Metal.

Metal Water Piping. The metal water piping system shall be bonded as required in (A)(1), (A)(2), or (A)(3) of this section.
1. General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to any of the following:Service equipment enclosureGrounded conductor at the serviceGrounding electrode conductor if of sufficient sizeOne or more grounding electrodes used, if the ground‐ ing electrode conductor or bonding jumper to the grounding electrode is of sufficient size(1)
4. The bonding jumper(s) shall be installed in accordance with 250.64(A), 250.64(B), and 250.64(E). The points of attach‐ ment of the bonding jumper(s) shall be accessible. The bond‐ ing jumper(s) shall be sized in accordance with Table
  Over 1100 Over 1750 See Notes 1 and 2.Notes:
  1. If the ungrounded supply conductors are larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded conductor or bonding jumper shall have an area not less than 121∕2 percent of the area of the largest ungrounded supply conductor or equivalent area for parallel supply conductors. The grounded conductor or bonding jumper shall not be required to be larger than the largest ungrounded conductor or set of ungrounded conductors.are larger than 1100 kcmil
  2. If the ungrounded supply conductorscopper or 1750 kcmil aluminum and if the ungrounded supply conductors and the bonding jumper are of different materials (copper, aluminum, or copper-clad aluminum), the minimum size of the grounded conductor or bonding jumper shall be based on the assumed use of ungrounded supply conductors of the same material as the grounded conductor or bonding jumper and will have an ampacity equivalent to that of the installed ungrounded supply conductors.
  3. If multiple sets of service-entrance conductors are used as permitted in 230.40, Exception No. 2, or if multiple sets of ungrounded supply conductors are installed for a separately derived system, the equivalent size of the largest ungrounded supply conductor(s) shall be determined by the largest sum of the areas of the corresponding conductors of each set.
  4. If there are no service-entrance conductors, the supply conductor size shall be determined by the equivalent size of the largest service- entrance conductor required for the load to be served.
  *For the purposes of applying this table and its notes, the term bonding jumper refers to main bonding jumpers, system bonding jumpers, and supply-side bonding jumpers.•250.102(C)(1) except as permitted in 250.104(A)(2) and 250.104(A)(3).
  1. Buildings of Multiple Occupancy. In buildings of multiple occupancy where the metal water piping system(s) installed in or attached to a building or structure for the individual occu‐ pancies is metallically isolated from all other occupancies by use of nonmetallic water piping, the metal water piping system(s) for each occupancy shall be permitted to be bonded
    to the equipment grounding terminal of the switchgear, switch‐ board, or panelboard enclosure (other than service equip‐ ment) supplying that occupancy. The bonding jumper shall be sized in accordance with 250.102(D).
  2. Multiple Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). The metal water piping system(s) installed in or attached to a building or structure shall be bonded to any of the following:
  1. Building or structure disconnecting means enclosure where located at the building or structure
  2. Equipment grounding conductor run with the supply conductors
  3. One or more grounding electrodes used
  The bonding jumper(s) shall be sized in accordance with Table 250.102(C)(1), based on the size of the feeder or branch- circuit conductors that supply the building or structure. The bonding jumper shall not be required to be larger than the largest ungrounded feeder or branch-circuit conductor supply‐ ing the building or structure.
Other Metal Piping. If installed in or attached to a build‐ ing or structure, a metal piping system(s), including gas piping, that is likely to become energized shall be bonded to any of the following:
1. Equipment grounding conductor for the circuit that is likely to energize the piping system
2. Service equipment enclosure
3. Grounded conductor at the service
4. Grounding electrode conductor, if of sufficient size
5. One or more grounding electrodes used, if the ground‐ ing electrode conductor or bonding jumper to the grounding electrode is of sufficient size
The bonding conductor(s) or jumper(s) shall be sized in accordance with Table 250.122, and equipment grounding conductors shall be sized in accordance with Table 250.122 using the rating of the circuit that is likely to energize the piping system(s). The points of attachment of the bonding jumper(s) shall be accessible.Informational Note No. 1: Bonding all piping and metal air ducts within the premises will provide additional safety.Informational Note No. 2: Additional information for gas piping systems can be found in Section 7.13 of NFPA 54 -2015, National Fuel Gas Code.
1. Service equipment enclosure
2. Grounded conductor at the service
3. Disconnecting means for buildings or structures supplied by a feeder or branch circuit
4. Grounding electrode conductor, if of sufficient size
5. One or more grounding electrodes used, if the ground‐ ing electrode conductor or bonding jumper to the grounding electrode is of sufficient size
Structural Metal. Exposed structural metal that is inter‐ connected to form a metal building frame and is not intention‐ ally grounded or bonded and is likely to become energized shall be bonded to any of the following:
The bonding conductor(s) or jumper(s) shall be sized in accordance with Table 250.102(C)(1) and installed in accord‐ ance with 250.64(A), 250.64(B), and 250.64(E). The points of attachment of the bonding jumper(s) shall be accessible unless installed in compliance with 250.68(A) Exception No. 2.
Separately Derived Systems. Metal water piping systems and structural metal that is interconnected to form a building frame shall be bonded to separately derived systems in accord‐ ance with 250.104(D)(1) through 250.104(D)(3).
1. Metal Water Piping System(s). The grounded conductor of each separately derived system shall be bonded to the near‐ est available point of the metal water piping system(s) in the area served by each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.102(C)(1) based on the largest ungrounded conductor of the separately derived system.Exception No. 1: A separate bonding jumper to the metal water piping system shall not be required if the metal water piping system is used as the grounding electrode for the separately derived system and the water piping system is in the area served.Exception No. 2: A separate water piping bonding jumper shall not be required if the metal frame of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the metal water piping in the area served by the separately derived system.
2. Structural Metal. If exposed structural metal that is inter‐ connected to form the building frame exists in the area served by the separately derived system, it shall be bonded to the grounded conductor of each separately derived system. This connection shall be made at the same point on the separately derived system where the grounding electrode conductor is connected. Each bonding jumper shall be sized in accordance with Table 250.102(C)(1) based on the largest ungrounded conductor of the separately derived system.Exception No. 1: A separate bonding jumper to the building structural metal shall not be required if the metal frame of a building or structure is used as the grounding electrode for the separately derived system.Exception No. 2: A separate bonding jumper to the building structural metal shall not be required if the water piping of a building or structure is used as the grounding electrode for a separately derived system and is bonded to the building structural metal in the area served by the sepa‐ rately derived system.
3. Common Grounding Electrode Conductor. If a common grounding electrode conductor is installed for multiple sepa‐ rately derived systems as permitted by 250.30(A)(6), and exposed structural metal that is interconnected to form the building frame or interior metal piping exists in the area served by the separately derived system, the metal piping and the structural metal member shall be bonded to the common grounding electrode conductor in the area served by the sepa‐ rately derived system.

Exception: A separate bonding jumper from each derived system to metal water piping and to structural metal members shall not be required if the metal water piping and the structural metal members in the area served by the separately derived system are bonded to the common grounding electrode conductor.

250.106 Lightning Protection Systems. The lightning protec‐ tion system ground terminals shall be bonded to the building or structure grounding electrode system.

Informational Note No. 1: See 250.60 for use of strike termina‐ tion devices. For further information, see NFPA 780-2014, Stand‐ ard for the Installation of Lightning Protection Systems, which

contains detailed information on grounding, bonding, and side‐ flash distance from lightning protection systems.

Informational Note No. 2: Metal raceways, enclosures, frames, and other non–current-carrying metal parts of electrical equip‐ ment installed on a building equipped with a lightning protec‐ tion system may require bonding or spacing from the lightning protection conductors in accordance with NFPA 780-2014, Standard for the Installation of Lightning Protection Systems.

Part VI. Equipment Grounding and Equipment Grounding Conductors

250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Exposed, normally non–current- carrying metal parts of fixed equipment supplied by or enclos‐ ing conductors or components that are likely to become energized shall be connected to an equipment grounding conductor under any of the following conditions:

Where within 2.5 m (8 ft) vertically or 1.5 m (5 ft) hori‐ zontally of ground or grounded metal objects and subject to contact by persons
Where located in a wet or damp location and not isolated
Where in electrical contact with metal
Where in a hazardous (classified) location as covered by Articles 500 through 517
Where supplied by a wiring method that provides an equipment grounding conductor, except as permitted by 250.86, Exception No. 2, for short sections of metal enclo‐ sures
Where equipment operates with any terminal at over 150 volts to ground

Exception No. 1: If exempted by special permission, the metal frame of electrically heated appliances that have the frame permanently and effectively insulated from ground shall not be required to be grounded.

Exception No. 2: Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles at a height exceeding 2.5 m (8 ft) above ground or grade level shall not be required to be grounded.

Exception No. 3: Listed equipment protected by a system of double insu‐ lation, or its equivalent, shall not be required to be connected to the equipment grounding conductor. Where such a system is employed, the equipment shall be distinctively marked.

250.112 Specific Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods. Except as permit‐ ted in 250.112(F) and (I), exposed, normally non–current- carrying metal parts of equipment described in 250.112(A) through (K), and normally non–current-carrying metal parts of equipment and enclosures described in 250.112(L) and (M), shall be connected to an equipment grounding conductor, regardless of voltage.

Switchgear and Switchboard Frames and Structures. Switchgear or switchboard frames and structures supporting switching equipment, except frames of 2-wire dc switchgear or switchboards where effectively insulated from ground.
Pipe Organs. Generator and motor frames in an electri‐ cally operated pipe organ, unless effectively insulated from ground and the motor driving it.
Motor Frames. Motor frames, as provided by 430.242.
Enclosures for Motor Controllers. Enclosures for motor controllers unless attached to ungrounded portable equip‐ ment.
Elevators and Cranes. Electrical equipment for elevators and cranes.
Garages, Theaters, and Motion Picture Studios. Electrical equipment in commercial garages, theaters, and motion picture studios, except pendant lampholders supplied by circuits not over 150 volts to ground.
Electric Signs. Electric signs, outline lighting, and associ‐ ated equipment as provided in 600.7.
Motion Picture Projection Equipment. Motion picture projection equipment.
Remote-Control, Signaling, and Fire Alarm Circuits. Equipment supplied by Class 1 circuits shall be grounded unless operating at less than 50 volts. Equipment supplied by Class 1 power-limited circuits, by Class 2 and Class 3 remote- control and signaling circuits, and by fire alarm circuits shall be grounded where system grounding is required by Part II or Part VIII of this article.
Luminaires. Luminaires as provided in Part V of Arti‐ cle 410.
Skid-Mounted Equipment. Permanently mounted electri‐ cal equipment and skids shall be connected to the equipment grounding conductor sized as required by 250.122.
Motor-Operated Water Pumps. Motor-operated water pumps, including the submersible type.
Metal Well Casings. Where a submersible pump is used in a metal well casing, the well casing shall be connected to the pump circuit equipment grounding conductor.

250.114 Equipment Connected by Cord and Plug. Under any of the conditions described in 250.114(1) through (4), exposed, normally non–current-carrying metal parts of cord- and-plug-connected equipment shall be connected to the equipment grounding conductor.

Exception: Listed tools, listed appliances, and listed equipment covered in 250.114(2) through (4) shall not be required to be connected to an equipment grounding conductor where protected by a system of double insulation or its equivalent. Double insulated equipment shall be distinctively marked.

In hazardous (classified) locations (see Articles 500 through 517)
Where operated at over 150 volts to groundException No. 1: Motors, where guarded, shall not be required to be connected to an equipment grounding conductor.Exception No. 2: Metal frames of electrically heated appliances, exemp‐ ted by special permission, shall not be required to be connected to an equipment grounding conductor, in which case the frames shall be permanently and effectively insulated from ground.
In residential occupancies:
1. Refrigerators, freezers, and air conditioners
2. Clothes-washing, clothes-drying, dish-washing machines; ranges; kitchen waste disposers; informa‐ tion technology equipment; sump pumps and electri‐ cal aquarium equipment
3. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor- operated tools
4. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
5. Portable handlamps
In other than residential occupancies:
1. Refrigerators, freezers, and air conditioners
2. Clothes-washing, clothes-drying, dish-washing machines; information technology equipment; sump pumps and electrical aquarium equipment
3. Hand-held motor-operated tools, stationary and fixed motor-operated tools, and light industrial motor- operated tools
4. Motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers
5. Portable handlamps
6. Cord-and-plug-connected appliances used in damp or wet locations or by persons standing on the ground or on metal floors or working inside of metal tanks or boilers
7. Tools likely to be used in wet or conductive locations

Exception: Tools and portable handlamps likely to be used in wet or conductive locations shall not be required to be connected to an equipment grounding conductor where supplied through an isolat‐ ing transformer with an ungrounded secondary of not over 50 volts.

250.116 Nonelectrical Equipment. The metal parts of the following nonelectrical equipment described in this section shall be connected to the equipment grounding conductor:

Frames and tracks of electrically operated cranes and hoists
Frames of nonelectrically driven elevator cars to which electrical conductors are attached
Hand-operated metal shifting ropes or cables of electric elevators

Informational Note: Where extensive metal in or on buildings or structures may become energized and is subject to personal contact, adequate bonding and grounding will provide addi‐ tional safety.

Types of Equipment Grounding Conductors. The equipment grounding conductor run with or enclosing the circuit conductors shall be one or more or a combination of the following:
1. A copper, aluminum, or copper-clad aluminum conduc‐ tor. This conductor shall be solid or stranded; insulated, covered, or bare; and in the form of a wire or a busbar of any shape.
2. Rigid metal conduit.
3. Intermediate metal conduit.
4. Electrical metallic tubing.
5. Listed flexible metal conduit meeting all the following conditions:
  1. The conduit is terminated in listed fittings.c. The size of the conduit does not exceed metric desig‐nator 35 (trade size 11∕4).
  2. The circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
    1. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
    2. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equip‐ ment that requires movement after installation, an equipment grounding conductor shall be installed.
6. Listed liquidtight flexible metal conduit meeting all the following conditions:
  1. The conduit is terminated in listed fittings.
  2. For metric designators 12 through 16 (trade sizes 3∕8 through 1∕2), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
  3. For metric designators 21 through 35 (trade sizes 3∕4 through 11∕4), the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flex‐ ible metal conduit, flexible metallic tubing, or liquid‐ tight flexible metal conduit in trade sizes metric designators 12 through 16 (trade sizes 3∕8 through 1∕2) in the ground-fault current path.
  4. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
  5. If used to connect equipment where flexibility is necessary to minimize the transmission of vibration from equipment or to provide flexibility for equip‐ ment that requires movement after installation, an equipment grounding conductor shall be installed.
7. Flexible metallic tubing where the tubing is terminated in listed fittings and meeting the following conditions:
  1. The circuit conductors contained in the tubing are protected by overcurrent devices rated at 20 amperes or less.
  2. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground-fault current path does not exceed 1.8 m (6 ft).
8. Armor of Type AC cable as provided in 320.108.
9. The copper sheath of mineral-insulated, metal-sheathed cable Type MI.
10. Type MC cable that provides an effective ground-fault current path in accordance with one or more of the following:
  1. It contains an insulated or uninsulated equipment grounding conductor in compliance with 250.118(1).
  2. The combined metallic sheath and uninsulated equipment grounding/bonding conductor of inter‐ locked metal tape–type MC cable that is listed and identified as an equipment grounding conductor
  3. The metallic sheath or the combined metallic sheath and equipment grounding conductors of the smooth or corrugated tube-type MC cable that is listed and identified as an equipment grounding conductor
11. Cable trays as permitted in 392.10 and 392.60.
12. Cablebus framework as permitted in 370.60(1).
13. Other listed electrically continuous metal raceways and listed auxiliary gutters.
14. Surface metal raceways listed for grounding.
Informational Note: For a definition of Effective Ground-Fault Current Path, see Article 100.
Identification of Equipment Grounding Conductors. Unless required elsewhere in this Code, equipment grounding conductors shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes except as permitted in this section. Conductors with insulation or indi‐ vidual covering that is green, green with one or more yellow stripes, or otherwise identified as permitted by this section shall not be used for ungrounded or grounded circuit conductors.Exception No. 1: Power-limited Class 2 or Class 3 cables, power-limited fire alarm cables, or communications cables containing only circuits operating at less than 50 volts where connected to equipment not required to be grounded in accordance with 250.112(I) shall be permit‐ ted to use a conductor with green insulation or green with one or more yellow stripes for other than equipment grounding purposes.Exception No. 2: Flexible cords having an integral insulation and jacket without an equipment grounding conductor shall be permitted to have a continuous outer finish that is green.Informational Note: An example of a flexible cord with integral- type insulation is Type SPT-2, 2 conductor.Exception No. 3: Conductors with green insulation shall be permitted to be used as ungrounded signal conductors where installed between the output terminations of traffic signal control and traffic signal indicat‐ ing heads. Signaling circuits installed in accordance with this exception shall include an equipment grounding conductor in accordance with250.118. Wire-type equipment grounding conductors shall be bare or have insulation or covering that is green with one or more yellow stripes.
1. Conductors 4 AWG and Larger. Equipment grounding conductors 4 AWG and larger shall comply with 250.119(A)(1) and (A)(2).
  1. An insulated or covered conductor 4 AWG and larger shall be permitted, at the time of installation, to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor is accessible.Exception: Conductors 4 AWG and larger shall not be required to be marked in conduit bodies that contain no splices or unused hubs.
  2. Identification shall encircle the conductor and shall be accomplished by one of the following:
    1. Stripping the insulation or covering from the entire exposed length
    2. Coloring the insulation or covering green at the termination
    3. Marking the insulation or covering with green tape or green adhesive labels at the termination
2. Multiconductor Cable. Where the conditions of mainte‐ nance and supervision ensure that only qualified persons serv‐ ice the installation, one or more insulated conductors in a multiconductor cable, at the time of installation, shall be permitted to be permanently identified as equipment ground‐ ing conductors at each end and at every point where the conductors are accessible by one of the following means:
  1. Stripping the insulation from the entire exposed length.
  2. Coloring the exposed insulation green.
  3. Marking the exposed insulation with green tape or green adhesive labels. Identification shall encircle the conduc‐ tor.
3. Flexible Cord. Equipment grounding conductors in flexi‐ ble cords shall be insulated and shall have a continuous outer finish that is either green or green with one or more yellow stripes.
Equipment Grounding Conductor Installation. An equipment grounding conductor shall be installed in accord‐ ance with 250.120(A), (B), and (C).
1. Raceway, Cable Trays, Cable Armor, Cablebus, or Cable Sheaths. Where it consists of a raceway, cable tray, cable armor, cablebus framework, or cable sheath or where it is a wire within a raceway or cable, it shall be installed in accord‐ ance with the applicable provisions in this Code using fittings for joints and terminations approved for use with the type race‐ way or cable used. All connections, joints, and fittings shall be made tight using suitable tools.Informational Note: See the UL guide information on FHIT systems for equipment grounding conductors installed in a race‐ way that are part of an electrical circuit protective system or a fire-rated cable listed to maintain circuit integrity.
2. Aluminum and Copper-Clad Aluminum Conductors. Equipment grounding conductors of bare or insulated alumi‐ num or copper-clad aluminum shall be permitted. Bare conductors shall not come in direct contact with masonry or the earth or where subject to corrosive conditions. Aluminum or copper-clad aluminum conductors shall not be terminated within 450 mm (18 in.) of the earth.
3. Equipment Grounding Conductors Smaller Than 6 AWG. Where not routed with circuit conductors as permitted in 250.130(C) and 250.134(B) Exception No. 2, equipment grounding conductors smaller than 6 AWG shall be protected from physical damage by an identified raceway or cable armor unless installed within hollow spaces of the framing members of buildings or structures and where not subject to physical damage.
Use of Equipment Grounding Conductors. An equip‐ ment grounding conductor shall not be used as a grounding electrode conductor.Exception: A wire-type equipment grounding conductor installed in compliance with 250.6(A) and the applicable requirements for both the equipment grounding conductor and the grounding electrode conductor in Parts II, III, and VI of this article shall be permitted to serve as both an equipment grounding conductor and a grounding electrode conduc‐ tor.
Size of Equipment Grounding Conductors.

General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).
Equipment grounding conductors shall be permitted to be sectioned within a multiconductor cable, provided the combined circular mil area complies with Table 250.122.
Increased in Size. Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, where installed, shall be increased in size proportionately, according to the circular mil area of the ungrounded conductors.
Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway, cable, or cable tray, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).
Motor Circuits. Equipment grounding conductors for motor circuits shall be sized in accordance with (D)(1) or (D)(2).
1. General. The equipment grounding conductor size shall not be smaller than determined by 250.122(A) based on the rating of the branch-circuit short-circuit and ground-fault protective device.
2. Instantaneous-Trip Circuit Breaker and Motor Short-Circuit Protector. Where the overcurrent device is an instantaneous- trip circuit breaker or a motor short-circuit protector, the equipment grounding conductor shall be sized not smaller than that given by 250.122(A) using the maximum permitted rating of a dual element time-delay fuse selected for branch- circuit short-circuit and ground-fault protection in accordance with 430.52(C)(1), Exception No. 1.
Flexible Cord and Fixture Wire. The equipment ground‐ ing conductor in a flexible cord with the largest circuit conduc‐ tor 10 AWG or smaller, and the equipment grounding conductor used with fixture wires of any size in accordance with 240.5, shall not be smaller than 18 AWG copper and shall not be smaller than the circuit conductors. The equipment grounding conductor in a flexible cord with a circuit conduc‐ tor larger than 10 AWG shall be sized in accordance with Table 250.122.
Conductors in Parallel. For circuits of parallel conductors as permitted in 310.10(H), the equipment grounding conduc‐ tor shall be installed in accordance with (1) or (2).N
1. Conductor Installations in Raceways, Auxiliary Gutters, or Cable Trays.
  1. Single Raceway or Cable Tray. If conductors are instal‐ led in parallel in the same raceway or cable tray, a single wire- type conductor shall be permitted as the equipment grounding conductor. The wire-type equipment grounding conductor shall be sized in accordance with 250.122, based on the over‐ current protective device for the feeder or branch circuit. Wire- type equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c). Metal raceways or auxiliary gutters in accordance with 250.118 or cable trays complying with 392.60(B) shall be permitted as the equipment grounding conductor.
  2. Multiple Raceways. If conductors are installed in parallel in multiple raceways, wire-type equipment grounding conductors, where used, shall be installed in parallel in each raceway. The equipment grounding conductor installed in each raceway shall be sized in compliance with 250.122 basedon the overcurrent protective device for the feeder or branch circuit. Metal raceways or auxiliary gutters in accordance with250.118 or cable trays complying with 392.60(B) shall be permitted as the equipment grounding conductor.N
2. Multiconductor Cables.
  1. If multiconductor cables are installed in parallel, the equipment grounding conductor(s) in each cable shall be connected in parallel.
  2. If multiconductor cables are installed in parallel in the same raceway, auxiliary gutter, or cable tray, a single equip‐ ment grounding conductor that is sized in accordance with250.122 shall be permitted in combination with the equipment grounding conductors provided within the multiconductor cables and shall all be connected together.
  3. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c). Cable trays complying with 392.60(B), metal raceways in accordance with 250.118, or auxiliary gutters shall be permitted as the equipment grounding conductor.
  4. Except as provided in 250.122(F)(2)(b) for raceway or cable tray installations, the equipment grounding conductor in each multiconductor cable shall be sized in accordance with250.122 based on the overcurrent protective device for the feeder or branch circuit.
Feeder Taps. Equipment grounding conductors run with feeder taps shall not be smaller than shown in Table 250.122 based on the rating of the overcurrent device ahead of the feeder but shall not be required to be larger than the tap conductors.

250.124 Equipment Grounding Conductor Continuity.

Separable Connections. Separable connections such as those provided in drawout equipment or attachment plugs and mating connectors and receptacles shall provide for first-make, last-break of the equipment grounding conductor. First-make, last-break shall not be required where interlocked equipment, plugs, receptacles, and connectors preclude energization with‐ out grounding continuity.
Switches. No automatic cutout or switch shall be placed in the equipment grounding conductor of a premises wiring system unless the opening of the cutout or switch disconnects all sources of energy.250.126 Identification of Wiring Device Terminals. The terminal for the connection of the equipment grounding conductor shall be identified by one of the following:
1. A green, not readily removable terminal screw with a hexagonal head.
2. A green, hexagonal, not readily removable terminal nut.
3. A green pressure wire connector. If the terminal for the equipment grounding conductor is not visible, the conductor entrance hole shall be marked with the word green or ground, the letters G or GR, a grounding symbol, or otherwise identified by a distinctive green color. If the terminal for the equipment grounding conductor is read‐ ily removable, the area adjacent to the terminal shall be similarly marked.
Informational Note: See Informational Note Figure 250.126.
Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment
Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall

Rating or Setting of Automatic Overcurrent Device in Circuit Ahead

of Equipment, Conduit, etc., Not Exceeding

Size (AWG or kcmil)

Aluminum or Copper-Clad

be permitted to be connected to any of the following:

Any accessible point on the grounding electrode system as described in 250.50151412201210601081008620064300424003150021/060012/08001/03/010002/04/012003/025016004/035020002504002500350600300040060040005007505000700120060008001200
Any accessible point on the grounding electrode conduc‐ tor(Amperes)CopperAluminum*
The equipment grounding terminal bar within the enclo‐ sure where the branch circuit for the receptacle or branch circuit originates
An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
For grounded systems, the grounded service conductor within the service equipment enclosure
For ungrounded systems, the grounding terminal bar within the service equipment enclosure

Informational Note: See 406.4(D) for the use of a ground-fault circuit-interrupting type of receptacle.

250.132 Short Sections of Raceway. Isolated sections of metal raceway or cable armor, where required to be grounded, shall be connected to an equipment grounding conductor in accordance with 250.134.

250.134 Equipment Fastened in Place or Connected by Perma‐ nent Wiring Methods (Fixed) — Grounding. Unless grounded by connection to the grounded circuit conductor as permitted by 250.32, 250.140, and 250.142, non–current-carrying metal

Note: Where necessary to comply with 250.4(A)(5) or (B)(4), the equipment grounding conductor shall be sized larger than given in this table.

*See installation restrictions in 250.120.

Informational Note Figure 250.126 One Example of a Symbol Used to Identify the Grounding Termination Point for an Equipment Grounding Conductor.

Part VII. Methods of Equipment Grounding

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

For Grounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor.
For Ungrounded Systems. The connection shall be made by bonding the equipment grounding conductor to the grounding electrode conductor.

parts of equipment, raceways, and other enclosures, if groun‐ ded, shall be connected to an equipment grounding conductor by one of the methods specified in 250.134(A) or (B).

Equipment Grounding Conductor Types. By connecting to any of the equipment grounding conductors permitted by 250.118.
With Circuit Conductors. By connecting to an equipment grounding conductor contained within the same raceway, cable, or otherwise run with the circuit conductors.

Exception No. 1: As provided in 250.130(C), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

Exception No. 2: For dc circuits, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

Informational Note No. 1: See 250.102 and 250.168 for equip‐ ment bonding jumper requirements.

Informational Note No. 2: See 400.10 for use of cords for fixed equipment.

250.136 Equipment Considered Grounded. Under the condi‐ tions specified in 250.136(A) and (B), the normally non– current-carrying metal parts of the equipment shall be consid‐ ered grounded.

Equipment Secured to Grounded Metal Supports. Electri‐ cal equipment secured to and in electrical contact with a metal rack or structure provided for its support and connected to an equipment grounding conductor by one of the means indica‐ ted in 250.134. The structural metal frame of a building shall not be used as the required equipment grounding conductor for ac equipment.
Metal Car Frames. Metal car frames supported by metal hoisting cables attached to or running over metal sheaves or drums of elevator machines that are connected to an equip‐ ment grounding conductor by one of the methods indicated in 250.134.

250.138 Cord-and-Plug-Connected Equipment. Non–current- carrying metal parts of cord-and-plug-connected equipment, if grounded, shall be connected to an equipment grounding conductor by one of the methods in 250.138(A) or (B).

By Means of an Equipment Grounding Conductor. By means of an equipment grounding conductor run with the power supply conductors in a cable assembly or flexible cord properly terminated in a grounding-type attachment plug with one fixed grounding contact.Exception: The grounding contacting pole of grounding-type plug-in ground-fault circuit interrupters shall be permitted to be of the movable, self-restoring type on circuits operating at not over 150 volts between any two conductors or over 150 volts between any conductor and ground.
By Means of a Separate Flexible Wire or Strap. By means of a separate flexible wire or strap, insulated or bare, connec‐ ted to an equipment grounding conductor, and protected as well as practicable against physical damage, where part of equipment.

250.140 Frames of Ranges and Clothes Dryers. Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.
Grounding contacts of receptacles furnished as part of the equip‐ ment are bonded to the equipment.

250.142 Use of Grounded Circuit Conductor for Grounding Equipment.

Supply-Side Equipment. A grounded circuit conductor shall be permitted to ground non–current-carrying metal parts of equipment, raceways, and other enclosures at any of the following locations:
1. On the supply side or within the enclosure of the ac service-disconnecting means
2. On the supply side or within the enclosure of the main disconnecting means for separate buildings as provided in 250.32(B)
3. On the supply side or within the enclosure of the main disconnecting means or overcurrent devices of a sepa‐ rately derived system where permitted by 250.30(A)(1)
Load-Side Equipment. Except as permitted in 250.30(A)(1) and 250.32(B) Exception, a grounded circuit conductor shall not be used for grounding non–current- carrying metal parts of equipment on the load side of the serv‐ ice disconnecting means or on the load side of a separately derived system disconnecting means or the overcurrent devices for a separately derived system not having a main disconnect‐ ing means.

Exception No. 1: The frames of ranges, wall-mounted ovens, counter- mounted cooking units, and clothes dryers under the conditions permit‐ ted for existing installations by 250.140 shall be permitted to be connected to the grounded circuit conductor.

Exception No. 2: It shall be permissible to ground meter enclosures by connection to the grounded circuit conductor on the load side of the service disconnect where all of the following conditions apply:

No service ground-fault protection is installed.
All meter enclosures are located immediately adjacent to the serv‐ ice disconnecting means.
The size of the grounded circuit conductor is not smaller than the size specified in Table 250.122 for equipment grounding conduc‐ tors.

Exception No. 3: Direct-current systems shall be permitted to be groun‐ ded on the load side of the disconnecting means or overcurrent device in accordance with 250.164.

Exception No. 4: Electrode-type boilers operating at over 1000 volts shall be grounded as required in 490.72(E)(1) and 490.74.

250.144 Multiple Circuit Connections. Where equipment is grounded and is supplied by separate connection to more than one circuit or grounded premises wiring system, an equipment grounding conductor termination shall be provided for each such connection as specified in 250.134 and 250.138.

250.146 Connecting Receptacle Grounding Terminal to Box. An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a groun‐ ded box unless grounded as in 250.146(A) through (D). The equipment bonding jumper shall be sized in accordance with Table 250.122 based on the rating of the overcurrent device protecting the circuit conductors.

Surface-Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box or a contact yoke or device that complies with 250.146(B) shall be permitted to ground the receptacle to the box. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device that complies with 250.146(B) to ensure direct metal-to-metal contact. This provision shall not apply to cover-mounted recep‐ tacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle. A listed exposed work cover shall be permitted to be the grounding and bonding means when (1) the device is attached to the cover with at least two fasteners that are perma‐ nent (such as a rivet) or have a thread locking or screw or nut locking means and (2) when the cover mounting holes are located on a flat non-raised portion of the cover.
Contact Devices or Yokes. Contact devices or yokes designed and listed as self-grounding shall be permitted in
conjunction with the supporting screws to establish equipment bonding between the device yoke and flush-type boxes.
Floor Boxes. Floor boxes designed for and listed as providing satisfactory ground continuity between the box and the device shall be permitted.
Isolated Ground Receptacles. Where installed for the reduction of electrical noise (electromagnetic interference) on the grounding circuit, a receptacle in which the grounding terminal is purposely insulated from the receptacle mounting means shall be permitted. The receptacle grounding terminal shall be connected to an insulated equipment grounding conductor run with the circuit conductors. This equipment grounding conductor shall be permitted to pass through one or more panelboards without a connection to the panelboard grounding terminal bar as permitted in 408.40, Exception, so as to terminate within the same building or structure directly at an equipment grounding conductor terminal of the applicable derived system or service. Where installed in accordance with the provisions of this section, this equipment grounding conductor shall also be permitted to pass through boxes, wire‐ ways, or other enclosures without being connected to such enclosures.

Informational Note: Use of an isolated equipment grounding conductor does not relieve the requirement for grounding the raceway system and outlet box.

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes. If circuit conductors are spliced within a box or terminated on equipment within or supported by a box, all equipment grounding conductor(s) associated with any of those circuit conductors shall be connected within the box or to the box with devices suitable for the use in accordance with 250.8 and 250.148(A) through (E).

Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box.

Connections. Connections and splices shall be made in accordance with 110.14(B) except that insulation shall not be required.
Grounding Continuity. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, luminaire, or other device fed from the box does not interfere with or interrupt the grounding continuity.
Metal Boxes. A connection shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose, equipment listed for grounding, or a listed grounding device.
Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding.
Solder. Connections depending solely on solder shall not be used.

Part VIII. Direct-Current Systems

250.160 General. Direct-current systems shall comply with Part VIII and other sections of Article 250 not specifically inten‐ ded for ac systems.

250.162 Direct-Current Circuits and Systems to Be Grounded. Direct-current circuits and systems shall be grounded as provi‐ ded for in 250.162(A) and (B).

Two-Wire, Direct-Current Systems. A 2-wire, dc system supplying premises wiring and operating at greater than 60 volts but not greater than 300 volts shall be grounded.Exception No. 1: A system equipped with a ground detector and supply‐ ing only industrial equipment in limited areas shall not be required to be grounded where installed adjacent to or integral with the source of supply.Exception No. 2: A rectifier-derived dc system supplied from an ac system complying with 250.20 shall not be required to be grounded.Exception No. 3: Direct-current fire alarm circuits having a maximum current of 0.030 ampere as specified in Article 760, Part III, shall not be required to be grounded.
Three-Wire, Direct-Current Systems. The neutral conduc‐ tor of all 3-wire, dc systems supplying premises wiring shall be grounded.

250.164 Point of Connection for Direct-Current Systems.

Off-Premises Source. Direct-current systems to be groun‐ ded and supplied from an off-premises source shall have the grounding connection made at one or more supply stations. A grounding connection shall not be made at individual services or at any point on the premises wiring.
On-Premises Source. Where the dc system source is loca‐ ted on the premises, a grounding connection shall be made at one of the following:

The source
The first system disconnection means or overcurrent device
By other means that accomplish equivalent system protec‐ tion and that utilize equipment listed and identified for the use

Size of the Direct-Current Grounding Electrode Conductor. The size of the grounding electrode conductor for a dc system shall be as specified in 250.166(A) and (B), except as permitted by 250.166(C) through (E). The grounding elec‐ trode conductor for a dc system shall meet the sizing require‐ ments in this section but shall not be required to be larger than 3/0 copper or 250 kcmil aluminum.
1. Not Smaller Than the Neutral Conductor. Where the dc system consists of a 3-wire balancer set or a balancer winding with overcurrent protection as provided in 445.12(D), the grounding electrode conductor shall not be smaller than the neutral conductor and not smaller than 8 AWG copper or 6 AWG aluminum.
2. Not Smaller Than the Largest Conductor. Where the dc system is other than as in 250.166(A), the grounding electrode conductor shall not be smaller than the largest conductor supplied by the system, and not smaller than 8 AWG copper or 6 AWG aluminum.
3. Connected to Rod, Pipe, or Plate Electrodes. Where connected to rod, pipe, or plate electrodes as in 250.52(A)(5) or (A)(7), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 6 AWG copper wire or 4 AWG aluminum wire.
4. Connected to a Concrete-Encased Electrode. Where connected to a concrete-encased electrode as in 250.52(A)(3), that portion of the grounding electrode conductor that is the sole connection to the grounding electrode shall not be required to be larger than 4 AWG copper wire.
5. Connected to a Ground Ring. Where connected to a ground ring as in 250.52(A)(4), that portion of the grounding electrode conductor that is the sole connection to the ground‐ ing electrode shall not be required to be larger than the conductor used for the ground ring.
Direct-Current Ground-Fault Detection.
1. Ungrounded Systems. Ground-fault detection systems shall be required for ungrounded systems.
2. Grounded Systems. Ground-fault detection shall be permitted for grounded systems.
3. Marking. Direct-current systems shall be legibly marked to indicate the grounding type at the dc source or the first disconnecting means of the system. The marking shall be of sufficient durability to withstand the environment involved.
Informational Note: NFPA 70E -2015 identifies four dc ground‐ ing types in detail.
Direct-Current System Bonding Jumper. For direct- current systems that are to be grounded, an unspliced bonding jumper shall be used to connect the equipment grounding conductor(s) to the grounded conductor at the source or the first system disconnecting means where the system is grounded. The size of the bonding jumper shall not be smaller than the system grounding electrode conductor specified in 250.166 and shall comply with the provisions of 250.28(A), (B), and (C).
Ungrounded Direct-Current Separately Derived Systems. Except as otherwise permitted in 250.34 for portable and vehicle-mounted generators, an ungrounded dc separately derived system supplied from a stand-alone power source (such as an engine–generator set) shall have a grounding electrode conductor connected to an electrode that complies with Part III of this article to provide for grounding of metal enclo‐ sures, raceways, cables, and exposed non–current-carrying metal parts of equipment. The grounding electrode conductor connection shall be to the metal enclosure at any point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no discon‐ necting means or overcurrent devices.The size of the grounding electrode conductor shall be in accordance with 250.166.
Part IX. Instruments, Meters, and Relays
Instrument Transformer Circuits. Secondary circuits of current and potential instrument transformers shall be grounded where the primary windings are connected to

circuits of 300 volts or more to ground and, where installed on or in switchgear and on switchboards, shall be grounded irre‐ spective of voltage.

Exception No. 1: Circuits where the primary windings are connected to circuits of 1000 volts or less with no live parts or wiring exposed or accessible to other than qualified persons.

Exception No. 2: Current transformer secondaries connected in a three- phase delta configuration shall not be required to be grounded.

250.172 Instrument Transformer Cases. Cases or frames of instrument transformers shall be connected to the equipment grounding conductor where accessible to other than qualified persons.

Exception: Cases or frames of current transformers, the primaries of which are not over 150 volts to ground and that are used exclusively to supply current to meters.

250.174 Cases of Instruments, Meters, and Relays Operating at 1000 Volts or Less. Instruments, meters, and relays operat‐ ing with windings or working parts at 1000 volts or less shall be connected to the equipment grounding conductor as specified in 250.174(A), (B), or (C).

Not on Switchgear or Switchboards. Instruments, meters, and relays not located on switchgear or switchboards operating with windings or working parts at 300 volts or more to ground, and accessible to other than qualified persons, shall have the cases and other exposed metal parts connected to the equip‐ ment grounding conductor.
On Switchgear or Dead-Front Switchboards. Instruments, meters, and relays (whether operated from current and poten‐ tial transformers or connected directly in the circuit) on switch‐ gear or switchboards having no live parts on the front of the panels shall have the cases connected to the equipment grounding conductor.
On Live-Front Switchboards. Instruments, meters, and relays (whether operated from current and potential trans‐ formers or connected directly in the circuit) on switchboards having exposed live parts on the front of panels shall not have their cases connected to the equipment grounding conductor. Mats of insulating rubber or other suitable floor insulation shall be provided for the operator where the voltage to ground exceeds 150.

250.176 Cases of Instruments, Meters, and Relays — Operat‐ ing at 1000 Volts and Over. Where instruments, meters, and relays have current-carrying parts of 1000 volts and over to ground, they shall be isolated by elevation or protected by suit‐ able barriers, grounded metal, or insulating covers or guards. Their cases shall not be connected to the equipment ground‐ ing conductor.

Exception: Cases of electrostatic ground detectors where the internal ground segments of the instrument are connected to the instrument case and grounded and the ground detector is isolated by elevation.

250.178 Instrument Equipment Grounding Conductor. The equipment grounding conductor for secondary circuits of instrument transformers and for instrument cases shall not be smaller than 12 AWG copper or 10 AWG aluminum. Cases of instrument transformers, instruments, meters, and relays that are mounted directly on grounded metal surfaces of enclosures or grounded metal of switchgear or switchboard panels shall be

considered to be grounded, and no additional equipment grounding conductor shall be required.

Part X. Grounding of Systems and Circuits of over 1000 Volts

250.180 General. Where systems over 1000 volts are groun‐ ded, they shall comply with all applicable provisions of the preceding sections of this article and with 250.182 through 250.194, which supplement and modify the preceding sections.

250.182 Derived Neutral Systems. A system neutral point derived from a grounding transformer shall be permitted to be used for grounding systems over 1 kV.

250.184 Solidly Grounded Neutral Systems. Solidly grounded neutral systems shall be permitted to be either single point grounded or multigrounded neutral.

Neutral Conductor.
1. Insulation Level. The minimum insulation level for neutral conductors of solidly grounded systems shall be 600 volts.Exception No. 1: Bare copper conductors shall be permitted to be used for the neutral conductor of the following:
  1. Service-entrance conductors
  2. Service laterals or underground service conductors
  3. Direct-buried portions of feeders
  Exception No. 2: Bare conductors shall be permitted for the neutral conductor of overhead portions installed outdoors.Exception No. 3: The grounded neutral conductor shall be permitted to be a bare conductor if isolated from phase conductors and protected from physical damage.Informational Note: See 225.4 for conductor covering where within 3.0 m (10 ft) of any building or other structure.(2) Ampacity. The neutral conductor shall be of sufficient ampacity for the load imposed on the conductor but not less than 331∕3 percent of the ampacity of the phase conductors.Exception: In industrial and commercial premises under engineering supervision, it shall be permissible to size the ampacity of the neutral conductor to not less than 20 percent of the ampacity of the phase conductor.
Single-Point Grounded Neutral System. Where a single- point grounded neutral system is used, the following shall apply:
1. A single-point grounded neutral system shall be permit‐ ted to be supplied from (a) or (b):
  1. A separately derived system
  2. A multigrounded neutral system with an equipment grounding conductor connected to the multigroun‐ ded neutral conductor at the source of the single- point grounded neutral system
2. A grounding electrode shall be provided for the system.
3. A grounding electrode conductor shall connect the grounding electrode to the system neutral conductor.
4. A bonding jumper shall connect the equipment ground‐ ing conductor to the grounding electrode conductor.
5. An equipment grounding conductor shall be provided to each building, structure, and equipment enclosure.
6. A neutral conductor shall only be required where phase- to-neutral loads are supplied.
7. The neutral conductor, where provided, shall be insula‐ ted and isolated from earth except at one location.
8. An equipment grounding conductor shall be run with the phase conductors and shall comply with (a), (b), and (c):
  1. Shall not carry continuous load
  2. May be bare or insulated
  3. Shall have sufficient ampacity for fault current duty
Multigrounded Neutral Systems. Where a multigrounded neutral system is used, the following shall apply:

The neutral conductor of a solidly grounded neutral system shall be permitted to be grounded at more than one point. Grounding shall be permitted at one or more of the following locations:
1. Transformers supplying conductors to a building or other structure
2. Underground circuits where the neutral conductor is exposed
3. Overhead circuits installed outdoors
The multigrounded neutral conductor shall be grounded at each transformer and at other additional locations by connection to a grounding electrode.
At least one grounding electrode shall be installed and connected to the multigrounded neutral conductor every 400 m (1300 ft).
The maximum distance between any two adjacent electro‐ des shall not be more than 400 m (1300 ft).
In a multigrounded shielded cable system, the shielding shall be grounded at each cable joint that is exposed to personnel contact.

Grounding Service-Supplied Alternating-Current Systems.
1. Systems with a Grounded Conductor at the Service Point. Where an ac system is grounded at any point and is provided with a grounded conductor at the service point, a grounded conductor(s) shall be installed and routed with the ungroun‐ ded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conduc‐ tor(s) terminal or bus. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means’s enclosure. The grounded conductor(s) shall be instal‐ led in accordance with 250.186(A)(1) through (A)(4). The size of the solidly grounded circuit conductor(s) shall be the larger of that determined by 250.184 or 250.186(A)(1) or (A)(2).Exception: Where two or more service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to connect the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.
  1. Sizing for a Single Raceway or Overhead Conductor. The grounded conductor shall not be smaller than the required grounding electrode conductor specified in Table 250.102(C)(1) but shall not be required to be larger than the largest ungrounded service-entrance conductor(s).
  2. Parallel Conductors in Two or More Raceways or Over‐ head Conductors. If the ungrounded service-entrance conductors are installed in parallel in two or more raceways or as overhead parallel conductors, the grounded conductors
    shall also be installed in parallel. The size of the grounded conductor in each raceway or overhead shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway or overhead, as indicated in 250.186(A)(1), but not smaller than 1/0 AWG.Informational Note: See 310.10(H) for grounded conductors connected in parallel.
  3. Delta-Connected Service. The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.
  4. Impedance Grounded Neutral Systems. Impedance grounded neutral systems shall be installed in accordance with 250.187.
2. Systems Without a Grounded Conductor at the Service Point. Where an ac system is grounded at any point and is not provided with a grounded conductor at the service point, a supply-side bonding jumper shall be installed and routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means equipment grounding conductor terminal or bus. The supply- side bonding jumper shall be installed in accordance with 250.186(B)(1) through (B)(3).Exception: Where two or more service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to connect the supply-side bonding jumper to the assembly common equipment grounding terminal or bus.
  1. Sizing for a Single Raceway or Overhead Conductor. The supply-side bonding jumper shall not be smaller than the required grounding electrode conductor specified in Table 250.102(C)(1) but shall not be required to be larger than the largest ungrounded service-entrance conductor(s).
  2. Parallel Conductors in Two or More Raceways or Over‐ head Conductors. If the ungrounded service-entrance conductors are installed in parallel in two or more raceways or overhead conductors, the supply-side bonding jumper shall also be installed in parallel. The size of the supply-side bonding jumper in each raceway or overhead shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway or overhead, as indicated in 250.186(A)(1), but not smaller than 1/0 AWG.
  3. Impedance Grounded Neutral Systems. Impedance grounded neutral systems shall be installed in accordance with 250.187.
Impedance Grounded Neutral Systems. Impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current shall be permitted where all of the following conditions are met:
1. The conditions of maintenance and supervision ensure that only qualified persons service the installation.
2. Ground detectors are installed on the system.
3. Line-to-neutral loads are not served.
Impedance grounded neutral systems shall comply with the provisions of 250.187(A) through (D).
1. Location. The grounding impedance shall be inserted in the grounding electrode conductor between the grounding electrode of the supply system and the neutral point of the supply transformer or generator.
2. Identified and Insulated. The neutral conductor shall comply with both of the following:
  1. The neutral conductor shall be identified.
  2. The neutral conductor shall be insulated for the maxi‐ mum neutral voltage.
  Informational Note: The maximum neutral voltage in a three-phase wye system is 57.7 percent of the phase-to-phase voltage.
3. System Neutral Conductor Connection. The system neutral conductor shall not be connected to ground, except through the neutral grounding impedance.
4. Equipment Grounding Conductors. Equipment ground‐ ing conductors shall be permitted to be bare and shall be elec‐ trically connected to the ground bus and grounding electrode conductor.
Grounding of Systems Supplying Portable or Mobile Equipment. Systems supplying portable or mobile equipment over 1000 volts, other than substations installed on a temporary basis, shall comply with 250.188(A) through (F).

Portable or Mobile Equipment. Portable or mobile equip‐ ment over 1000 volts shall be supplied from a system having its neutral conductor grounded through an impedance. Where a delta-connected system over 1000 volts is used to supply porta‐ ble or mobile equipment, a system neutral point and associated neutral conductor shall be derived.
Exposed Non–Current-Carrying Metal Parts. Exposed non–current-carrying metal parts of portable or mobile equip‐ ment shall be connected by an equipment grounding conduc‐ tor to the point at which the system neutral impedance is grounded.
Ground-Fault Current. The voltage developed between the portable or mobile equipment frame and ground by the flow of maximum ground-fault current shall not exceed 100 volts.
Ground-Fault Detection and Relaying. Ground-fault detection and relaying shall be provided to automatically de- energize any component of a system over 1000 volts that has developed a ground fault. The continuity of the equipment grounding conductor shall be continuously monitored so as to automatically de-energize the circuit of the system over 1000 volts to the portable or mobile equipment upon loss of continuity of the equipment grounding conductor.
Isolation. The grounding electrode to which the portable or mobile equipment system neutral impedance is connected shall be isolated from and separated in the ground by at least6.0 m (20 ft) from any other system or equipment grounding electrode, and there shall be no direct connection between the grounding electrodes, such as buried pipe and fence, and so forth.
Trailing Cable and Couplers. Trailing cable and couplers of systems over 1000 volts for interconnection of portable or mobile equipment shall meet the requirements of Part III of Article 400 for cables and 490.55 for couplers.

Grounding of Equipment.
1. Equipment Grounding. All non–current-carrying metal parts of fixed, portable, and mobile equipment and associated fences, housings, enclosures, and supporting structures shall be grounded.ARTICLE 280 — SURGE ARRESTERS, OVER 1000 VOLTS 280.4
  Exception: Where isolated from ground and located such that any person in contact with ground cannot contact such metal parts when the equipment is energized, the metal parts shall not be required to be grounded.Informational Note: See 250.110, Exception No. 2, for pole- mounted distribution apparatus.
2. Grounding Electrode Conductor. If a grounding elec‐ trode conductor connects non–current-carrying metal parts to ground, the grounding electrode conductor shall be sized in accordance with Table 250.66, based on the size of the largest ungrounded service, feeder, or branch-circuit conductors supplying the equipment. The grounding electrode conductor shall not be smaller than 6 AWG copper or 4 AWG aluminum.
3. Equipment Grounding Conductor. Equipment grounding conductors shall comply with 250.190(C)(1) through (C)(3).
  1. General. Equipment grounding conductors that are not an integral part of a cable assembly shall not be smaller than 6 AWG copper or 4 AWG aluminum.
  2. Shielded Cables. The metallic insulation shield encircling the current carrying conductors shall be permitted to be used as an equipment grounding conductor, if it is rated for clearing time of ground-fault current protective device operation with‐ out damaging the metallic shield. The metallic tape insulation shield and drain wire insulation shield shall not be used as an equipment grounding conductor for solidly grounded systems.
  3. Sizing. Equipment grounding conductors shall be sized in accordance with Table 250.122 based on the current rating of the fuse or the overcurrent setting of the protective relay.
Informational Note: The overcurrent rating for a circuit breaker is the combination of the current transformer ratio and the current pickup setting of the protective relay.
Grounding System at Alternating-Current Substations. For ac substations, the grounding system shall be in accordance with Part III of Article 250.

Informational Note: For further information on outdoor ac substation grounding, see IEEE 80-2013, IEEE Guide for Safety in AC Substation Grounding.

250.194 Grounding and Bonding of Fences and Other Metal Structures. Metallic fences enclosing, and other metal struc‐ tures in or surrounding, a substation with exposed electrical conductors and equipment shall be grounded and bonded to limit step, touch, and transfer voltages.

Metal Fences. Where metal fences are located within 5 m (16 ft) of the exposed electrical conductors or equipment, the fence shall be bonded to the grounding electrode system with wire-type bonding jumpers as follows:
1. Bonding jumpers shall be installed at each fence corner and at maximum 50 m (160 ft) intervals along the fence.
2. Where bare overhead conductors cross the fence, bond‐ ing jumpers shall be installed on each side of the cross‐ ing.
3. Gates shall be bonded to the gate support post, and each gate support post shall be bonded to the grounding elec‐ trode system.
4. Any gate or other opening in the fence shall be bonded across the opening by a buried bonding jumper.
5. The grounding grid or grounding electrode systems shall be extended to cover the swing of all gates.
6. The barbed wire strands above the fence shall be bonded to the grounding electrode system.
Alternate designs performed under engineering supervision shall be permitted for grounding or bonding of metal fences.Informational Note No. 1: A nonconducting fence or section may provide isolation for transfer of voltage to other areas.Informational Note No. 2: See IEEE 80-2013, IEEE Guide for Safety In AC Substation Grounding, for design and installation of fence grounding.
Metal Structures. All exposed conductive metal struc‐ tures, including guy wires within 2.5 m (8 ft) vertically or 5 m (16 ft) horizontally of exposed conductors or equipment and subject to contact by persons, shall be bonded to the ground‐ ing electrode systems in the area.

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